GEOLOGIC MAP OF THE SAN DIEGO COUNTY, CALIFORNIA: A ... · 5 7 6 65 88 77 68 73 52 86 63 73 81 87...
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5 7 6 65 88 77 68 73 52 86 63 73 81 87 73 88 87 86 81 72 68 60 75 87 75 83 85 86 85 83 80 88 87 88 75 74 89 77 82 83 87 83 87 87 87 84 82 72 77 68 80 83 72 70 82 76 72 75 82 77 54 82 81 80 79 63 73 86 82 84 78 69 77 70 72 75 74 87 83 82 86 73 75 77 73 82 67 71 Kjv Klp Kjv-w Kjv Klb/Kjv Kjv Ka Kcm Kjv Kjv Kc Kjv Tp Tp Klp Kcm Klb-w Ka-w Klp Ka Qya Klp-w Jcr Kjv Kc KJvs Kjv-w Kjv Tp? Ka Klp Klpm KJvs Kjv Tp Qya Kjv KJvs Qoc Kjv-w Klb/Kjv Kcm Klb-w Klb Ka Kc Kjv Qya Kjv-w Qya Ka KJvs Qya Klpm-w Kjv-w Klb Klpm-w Qoa af Qya Kjv Qya Qya Kjv-w Qw Qya Kc KJvs Kjv-w Klb-w Klp Kcm Klpm-w Kc Qya Qoc Klp Jcr Qya Kjv Klpm-w Klp-w Klpm Kjv Kjv-w Kjv-w Klp-w Kcm Kjv-w Kjv-w Qoa Qya Klb-w Klp-w Kjv Kjv Klp Kjv-w Tp Klb-w Kjv Jcr Kcm Jcr-w Kjv-w Klpm-w Qw Klp-w Kjv Ka Tp Kjv-w Qya Qoa Klp-w Qya Qya Klb-w Qya Qols? Ka Klb/Kjv Kmv Kjv-w Kjv Qya Klb Qoa Kjv-w Kjv-w Kmv Ka Ka Qya Ka-w Tp Qya Kmv Klb Qya Klpm-w Qoc Kjv-w Kc Kjv-w Kjv-w Klpm Ka Klb/Kjv Kjv Qya Kc Klpm-w Kjv Kjv Kc Kjv-w Klp-w Jcr Kcm Kjv-w Kjv Kjv-w Kjv-w Tp Kmv KJvs KJvs Tp QTf Kcm Kjv Qya Ka Ka-w Qoa Qoc Qoc Qw Qya Klpm Qya Qya Kcm Kcm Qya QTf af Qya Qya Kcm Qya Kjv-w Qya KJvs KJvs Kcm Kmv Kjv-w Qya Qya Kc Qoc Qols Kcm QTf? QTf QTf QTf KJvs Klb Qya QTf Kcm Tp Kjv Kjv Kjv Klb/Kjv Kjv Klb Jcr Kjv Kjv Qya Ka Qols Qya Qya Qya Kjv Ka Qya Qya Qw Qols Kjv-w Kjv Qya Qya Qw Qya Qya Qya Kjv Klb Klb Qya Qya Qw Qya Qya References: The bedrock geology is partly modified from Merriam (1953). Abbott, P.L., and Smith, T.E., 1989, Sonora, Mexico, source for the Eocene Poway Conglomerate of southern California: Geology, v. 17, p. 329-332. Anderson, C.L., 1991, Zircon uranium-lead isotopic ages of the Santiago Peak Volcanics and spatially related plutons of the Peninsular Ranges batholith, southern California: San Diego State University, M.S. thesis, 111 p. Bellemen, G.J., and Merriam, R.H., 1958, Petrology and origin of the Poway Conglomerate, San Diego County, California: Geological Society of America Bulletin v. 69, no. 2, p. 199-220. Fig. 1, scale approximately 1:312,500. Everhart, D.L., 1951, Geology of the Cuyamaca Peak quadrangle, San Diego County, California: California Division of Mines Bulletin 159, p. 51-115. Foster, B.D., 1994, Origin and tectonic significance of Peninsular Ranges amphibolites: San Diego State University, M.S. thesis, 112 p. Gastil, G., and Bushee, J., 1961, Geology and geomorphology of eastern San Diego County, Field Trip No. 1, Road Log: Geological Society of America, Field Trip Guidebook, San Diego County, 57th Annual Meeting, San Diego State College, p. 13, geologic map no. 2. Kennedy, M.P., and Peterson, G.L., 1975, Geology of the San Diego metropolitan area, California; Section B, eastern San Diego metropolitan area: California Division of Mines and Geology Bulletin 200, p. 43-56, scale 1:24,000. Krummenacher, D., Gastil, R.G., Bushee, J., and Doupont, J., 1975, K-Ar apparent ages, Peninsula Ranges batholith, southern California and Baja California: Geological Society of America Bulletin, v. 86, p. 760-768. Larsen, E.S., 1948, Batholithic and associated rocks of Corona, Elsinore, and San Luis Rey quadrangles, southern California: Geological Society of America Memoir 29, 182 p. Merriam, R.H., 1941, A southern California ring-dike: American Journal of Science, v. 239, no. 5, p. 365-371. Merriam, R.H., 1946, Igneous and metamorphic rocks of the southwestern part of the Ramona (30') quadrangle, San Diego County, California: Geological Society of America Bulletin, vol. 57, no. 3, p. 233-260, pl. 1, scale 1:160:000. Later revisions by R.H. Merriam, 1954, in Geology of southern California: California Division of Mines and Geology Bulletin 170, Geologic Guide no. 5, map no. 10, scale 1:203,000 and R.H. Merriam, unpublished mapping in the Ramona quadrangle, 1951-1953. Merriam, R.H., 1948, Orbicular structures in aplite dikes near Ramona, California: American Journal of Science, v. 246, no. 3, p. 129-137, fig. 2, scale 1:20,000. Merriam, R.H., 1954, A typical portion of the southern California batholith, San Diego County, in Geology of southern California: California Division of Mines and Geology Bulletin 170, map sheet no. 22, scale 1:62,500. Merriam, R.H., 1958, Geology of the Santa Ysabel quadrangle, San Diego County: California Division of Mines and Geology Bulletin 177, pl. 1, scale 1:62,500. Miller, W.J., 1935, Geomorphology of the southern Peninsular Ranges of California: Bulletin of the Geological Society of America, v. 46, p. 1535-1562. Miller, F.S., 1937, Petrology of the San Marcos gabbro, southern California: Bulletin of the Geological Society of America, v. 48, no. 10, p. 1397-1426. Minch, J.A., 1972, The late Mesozoic-early Tertiary framework of continental sedimentation, northern Peninsular Ranges, Baja California, Mexico: University of California, Riverside, Ph.D. dissertation, 192 p. Ortega-Rivera, Amabel, 2003, Geochronological constraints on the history of the Peninsular Ranges batholith of Alta and Baja California; tectonic implications for western Mexico, in Johnson, S.E., Paterson, S.R., Fletcher, J.M., Girty, G.H., Kimbrough, D.L., and Martin-Barajas, A., editors, Tectonic evolution of northwestern Mexico and the southwestern USA: Geological Society of America Special Paper 374, p. 297-335. Simpson, D.R., 1965, Geology of the central part of the Ramona pegmatite district, San Diego County, California: California Division of Mines and Geology, Special Report 86, p. 3-23, (a) figure 1, scale 1:60,000, (b) figure 2, scale 1:9,000, (c) figure 4, scale 1:275, (d) figure 5, scale 1:150. Snee, L.W., Naeser, C.W., Naeser, N.D., Todd, V.R., and Morton, D.M., 1994, Preliminary 40Ar/39Ar and fission-track cooling ages of plutonic rocks across the Peninsular Ranges batholiths, southern California: Geological Society of America Abstracts with Programs, v. 26, no 2, p. 94. Steer, B.L., and Abbott, P.L., 1984, Paleohydrology of the Eocene Ballena Gravels, San Diego Country, California: Sedimentary Geology, v. 38, p. 181-216. Streckeisen, A.L., 1973, Plutonic rocks – Classification and nomenclature recommended by the IUGS Subcommission on Systematics of Igneous Rocks: Geotimes, v. 18, p. 26-30 Streckeisen, A.L., 1976, To each plutonic rock a proper name: Earth Science Reviews, v. 12, p. 1-33. Tan, S.S., 2002, Geologic map of the San Vicente Reservoir 7.5' quadrangle, San Diego County, California: A digital database: California Geological Survey Preliminary Geologic Map website, http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm, scale 1:24,000. Todd, V.R., 1977, Geologic map of the Cuyamaca Peak quadrangle, San Diego County, California: U.S. Geological Survey Open-File Report 77-405, 13 p., scale 1:24,000. Todd, V.R., 1983, Geologic map of the El Cajon Mountain quadrangle, San Diego County, California: U.S. Geological Survey Open-File Report 83-781, scale 1:24,000. Todd, V.R., and Shaw, S.E., 1985, S-type granitoids and an I-S line in the Peninsular Ranges batholith, southern California: Geology, v. 13, no. 4, p. 231-233. Todd, V.R., Shaw, S.E., and Hammarstrom, J.M., 2003, Cretaceous plutons of the Peninsular Ranges batholith, San Diego and westernmost Imperial counties, California: Intrusion across a Late Jurassic continental margin, in Johnson, S.E., Paterson, S.R., Fletcher, J.M., Girty, G.H., Kimbrough, D.L., and Martin-Barajas, A., editors, Tectonic evolution of northwestern Mexico and the southwestern USA: Geological Society of America Special Paper 374, p. 185-235. Todd, V.R., 2004, Preliminary geologic map of the El Cajon 30’ x 60’ quadrangle, Southern California: U.S. Geological Survey Open-File Report 2004-1361, 30 p., 2 plates, scale 1:100,000. Weber, F.H., JR., 1963, Geology and mineral resources of San Diego County, California: California Division of Mines and Geology County Report 3, 309 p. 78 79 76 67 371 79 86 Radec Oasis Ramona Banner Borrego Aguanga Rosemont Oak Grove San Ysidro San Felipe Pine Hills San Pasqual Mesa Grande SantaYsabel Warner Springs Holcomb Village Borrego Springs Vail Lake Aguanga Beauty Mtn. Bucksnort Mtn. Collins Valley Boucher Hill Palomar Observatory Warner Springs Hot Springs Mtn. Borrego Palm Canyon Tubb Canyon Ranchita Warners Ranch Mesa Grande Rodriguez Mtn. San Pasqual Ramona Santa Ysabel Julian Earthquake Valley Clark Lake NE Borrego Sink Clark Lake Rabbit Peak Oasis Mapping completed under STATEMAP FY 2005-06 FY 2004-05 FY 2002-03 CGS OFR 96-06 & CD 2000-08* *GIS data for the Tubb Canyon 7.5’ quadrangle available on CD - CGS CD 2000-08. Paper copy available as OFR 96-06. 5 Kilometers 5 Miles Quartz Syenite Quartz Monzonite Quartz Monzodiorite Syenite Monzonite Monzodiorite Alkali-feldspar Granite Tonalite Diorite Gabbro Syenogranite Granodiorite Monzogranite Quartz Diorite 90 65 35 10 5 20 60 Q Q A P 60 20 5 60 Granite Classification of plutonic rock types (from Streckeisen, 1973; 1976). A, alkali feldspar; P, plagioclase feldspar; Q, quartz. CORRELATION OF MAP UNITS Kc af QUATERNARY Pliocene Eocene Paleocene Holocene Pleistocene TERTIARY CENOZOIC MESOZOIC CRETACEOUS JURASSIC Qw Kmv Kmv Kmv Kmv Kmv Kmv Kmv Kmv Kmv Kmv Kmv Kmv Kmv Kmv Kmv Kmv Kmv Kmv Kmv Kcm Kmv Kmv Kmv Kmv Klb/Kjv KJvs Qya Klb Klb-w Ka Ka-w Kjv Kjv-w Kjv Kjv-w Jcr Jcr-w Klp-w Klp Klpm Klpm-w Qoc Qoa Qols Qols QTf Tp Strike and dip of sedimentary beds. 25 MAP SYMBOLS 25 Strike and dip of igneous foliation. Vertical igneous foliation. 25 Strike and dip of metamorphic foliation. Vertical metamorphic foliation. Contact between map units - Solid where accurately located, dashed where approximately located; dotted where conselaed; queried where existence is questionable. Fault - Dashed where approximately located; dotted where concealed. ? Landslide - arrow indicates principal direction of movement, queried where existence is questionable. Pegmatite dike of the Ramona pegmatite district. ? Aplite dike. Leucocratic dike; related to Klp. Leucocratic dike; related to Kcm. Artificial fill (late Holocene) - Includes concrete dam structure at Sutherland Lake, and mixtures of non- engineered fill consisting of sand, gravel, trash and debris at the Ramona Landfill. Wash deposits (late Holocene) - Unconsolidated sand and gravel deposited in active washes. Consists of light brownish-gray (2.5Y 6/2) to grayish-brown (10YR 5/2), fine- to medium-grained sand, silt, and coarse sand to fine gravel. Sand is angular to sub-angular, micaceous, and is primarily derived from local bedrock. Subject to localized reworking and new sediment deposition during winter storms. Young axial channel deposits (Holocene to late Pleistocene) - Unconsolidated to slightly consolidated sand and gravel deposited in marginal parts of active washes. Consists of grayish-brown (2.5Y 5/2) to dark grayish-brown (10YR 4/2), fluvial deposits of fine- to coarse-grained sand with minor silt, and minor fine to coarse gravel and cobbles. Gravel and cobbles are sub-rounded to rounded. In most areas, unit is slightly elevated above the active younger wash deposits. Old colluvial deposits (Late to middle Pleistocene) - Unconsolidated to well consolidated deposits of sediment, rock fragments and soil material deposited by creep and rainwash. Consists of brown (7.5YR 4/3) to (7.5YR 5/4), fine- to coarse-grained sand, clay, silt, and minor fine gravel. Mapped where thick enough to obscure underlying bedrock. Forms aprons along the base of slopes. Old alluvium (Late to middle Pleistocene) - Moderately consolidated silt, sand and gravel deposited in older fluvial system. Consists of thin- to medium-bedded sandstone and minor conglomerate. Occurs as moderately to highly dissected terraces above stream valleys and in highland valley canyons. Older landslide deposits (Pleistocene) - Slope-failure deposits consisting of poorly to moderately consolidated, poorly sorted rock fragments and soil material. May be susceptible to renewed slope movements. Fanglomerate (Quaternary or Tertiary(?)) - Moderately to well-indurated, massively bedded, poorly sorted to unsorted, micaceous, silty, fine- to medium-grained, brown (10YR5/3) arkosic sandstone. Matrix- supported angular (0.5 to 3 cm) clasts of locally derived pegmatitic rock common. Near its base, the deposit contains abundant clasts of angular pegmatitic material as much as 20 cm in maximum dimen- sion; rare broken Poway-type metavolcanic and quartzite cobble clasts up to 7 cm; and rounded, “rotten” granitic boulders. Boulders average 30 cm in diameter and exceed one meter in maximum dimension. Fossiliferous; fossils consist of root casts and other unidentified casts and debris. Occurs as debris flow and fan deposits at base of slopes and in small drainages. Poorly exposed, usually only observed in roadcuts and gullies. Desiccation cracks common. Queried Tertiary age assignment based on degree of induration, and stratigraphic position above crystalline basement and below deeply weathered, eroded, unindurated colluvium. May include deposits related to Ballena River system. Poway Group/Ballena Gravels (Eocene-Paleocene) - Remnant fluvial-channel deposits of the Ballena River system. Massively bedded conglomerates, conglomeratic sandstone, and minor beds and lenses of sandstone up to 300 feet thick. Predominantly well-rounded to subrounded, resistant, exotic “Poway- type” metavolcanic and quartzite clasts with minor amounts of weathered clasts of locally derived crystal- line basement in a well-consolidated sandy matrix. Poway-type clasts characteristically are gray to red, weakly metamorphosed, porphyritic rhyolite and dacite with feldspar and quartz phenocrysts. Maximum long-dimension of clasts in the Ramona quadrangle approaches three feet. Auriferous. Tonalite of La Posta (Cretaceous) - Rocks tentatively correlated with La Posta-type plutons of the eastern zone of the PRB. Consists of homogeneous, idiomorphic medium- to coarse-grained hornblende-biotite tonalite, trondhjemite (leucotonalite), and leucogranodiorite. The unit is in part equivalent to the La Posta Quartz Diorite of Miller (1935). La Posta rocks contain abundant white-weathering plagioclase and low color index (C.I.), which together impart a white color to the low platy outcrops of the unit. Also character- istic are: 1) light-gray quartz grains up to 1 cm+ of bipyramidal to ovoid shape, 2) euhedral, barrel-shaped biotite books (0.5- to 1-cm across by 1.5 cm in length), and 3) scattered 2- to 5-cm-long K-feldspar oikocrysts that appear as glassy reflective cleavages on weathered rock surfaces. Grains of pale-yellow euhedral sphene are commonly visible in hand sample. The La Posta unit consists of plagioclase, quartz, biotite ± hornblende ± K-feldspar; in granodiorite and monzogranite, K-feldspar equals or exceeds biotite. In the Ramona quadrangle, the tonalite of La Posta forms an outer pluton of the Ramona ring-dike structure located along the structure’s southern and western sides. Medium-grained leucotonalite and tonalite/granodiorite of this pluton display idiomorphic texture (due to hornblende and biotite phenocrysts), are quartz-rich, and contain K-feldspar oikocrysts and visible sphene. A small exposure in the northwest corner of the quadrangle is also underlain by Klp. The larger Klp pluton in the Ramona quadrangle is petrographically similar to the La Posta-type pluton south of the town of Alpine, which is the westernmost exposure of the unit in the El Cajon 1:100,000 quadrangle. The Klp pluton of the Ramona ring-dike structure appears to be the origin of numerous large pegmatite dikes that intrude the quadrangle’s northwest quarter. Klp-w – deeply weatherd Klp. Tonalite of La Posta, Mafic phase (Cretaceous) – Rocks that partially border the tonalite of La Posta in the Ramona quadrangle. The rocks assigned to the mafic phase of La Posta are mineralogically and textur- ally similar to La Posta rocks but are more mafic. Unit consists of light-gray-weathering, strongly foliated, fine- to medium-grained tonalite that is less resistant to erosion and therefore crops out less prominently than La Posta. Tonalite of the mafic phase contains subequal biotite and hornblende as single euhedral/subhedral phenocrysts (idiomorphic texture), abundant quartz, euhedral sphene, scarce K- feldspar oikocrysts, and few mafic inclusions. At one locality, the La Posta pluton contains an inclusion of the mafic phase near its margin. Rocks assigned to the mafic phase of La Posta are tentatively corre- lated with the informally named tonalite of Granite Mountain (Kgm; Todd, 1979), which composes large zoned plutons in the eastern zone of the PRB and also occurs as envelopes of varying size surrounding small La Posta-type plutons in the western zone (Todd, 2004). South of the Ramona quadrangle, the Granite Mountain unit has isotopic ages of 98 ± 3 Ma (L.T. Silver, oral commun., 1979) and 101 ± 2 Ma (D.L. Kimbrough, oral commun., 1992). These ages are slightly older than those of adjacent La Posta plutons. Klpm-w – deeply weatherd Klpm. Cuyamaca Gabbro (Cretaceous) - The Cuyamaca Gabbro (Everhart, 1951) is the name given to large gabbro plutons, smaller gabbro bodies, and gabbroic dikes in central and southern San Diego County. Most of the gabbro in the Ramona quadrangle occurs in small bodies and dikes within granitic rocks. These rocks are fine- to coarse-grained and dark colored on fresh surfaces but typically weather to form a reddish soil with sparse outcrop. Textures are magmatic with slight recrystallization. Although some outcrops appear massive, most are foliated to some extent. Some display a strong foliation due to recrystallized mafic minerals. Flow banding is present near contact zones. Most gabbros have abundant fine-grained anhedral orthopyroxene with scarce subhedral phenocrysts. Hornblende is poikilitic and interstitial. Plagioclase typically occurs as subhedral laths. Abundant opaque oxide occurs as disseminated intersti- tial grains and as inclusions in hornblende and plagioclase. Some rocks have larger subhedral grains of hornblende with cores that appear to be altered pyroxene. A more leucocratic variety of gabbro occurs either interlayered with or gradational to the more common mafic variety. This rock has less abundant mafic minerals and may have fine-grained interstitial quartz. Gabbro assigned to the Cuyamaca Gabbro (Kc) is present in a discontinuous series of small pod-like bodies that are part of the Ramona ring-dike structure. Conventional K-Ar analysis of hornblende from two gabbro plutons south of the Ramona quadrangle yielded cooling ages of 108 and 104 Ma. An U-Pb zircon age of 107± 2 Ma for the gabbro pluton that underlies Poser Mountain in the Viejas Mountain 7.5-minute quadrangle is essentially the same as the age of the Ka pluton at the latter’s nearby type locality (D. L. Kimbrough, oral commun., 1992). Corte Madera Monzogranite (Cretaceous) - Corte Madera rocks consist of medium- to coarse-grained biotite leucomonzogranite, leucogranodiorite, and syenogranite as well as abundant dikes of leucogranite, alaskite, pegmatite, and aplite. Outcrops of the unit weather white with a pinkish-orange (peach) hue. Scarce mafic grains in Corte Madera rocks form lenticular aggregates whose wide (0.5-2 cm) spacing imparts a distinctive spotted appearance to rock surfaces. Foliation fabrics in Kcm rocks range from weak magmatic to strong synmagmatic or post-magmatic (subsolidus). Monzogranite of the Kcm unit is com- posed of subequal quartz and plagioclase with lesser K-feldspar and biotite; about half of petrographic samples contain small relict hornblendes. Granodiorite consists of plagioclase, quartz, K-feldspar, and biotite. Major minerals of the syenogranite phase of the Kcm unit are K-feldspar, quartz, plagioclase, and biotite. Characteristically, quartz in all facies of the unit occurs as subequant to lenticular grains as long as 1 cm; in moderately strained rocks, quartz phenocrysts are partly recrystallized to subgrains, whereas in highly strained rocks, quartz occurs in lenticular multi-grain aggregates and ribbons >1 centimeter long. Corte Madera plutons typically comprise the most centrally located and latest intrusions in Cretaceous zoned plutonic complexes in the western zone of the PRB (Todd and others, 2003). In the southern part of the Ramona quadrangle, Kcm forms the Mt. Gower pluton and its fringing dikes and also occurs as small bodies and dikes in the Japatul Valley Tonalite. An U-Pb zircon age of 111± 2 Ma was reported for the central Corte Madera-type pluton that underlies El Cajon Mountain (D.L. Kimbrough, oral commun., 1992). Conventional K-Ar hornblende cooling ages of 105 and 102 Ma were determined for two addi- tional plutons of the unit. Tonalite of Alpine (Cretaceous) - Consists of medium- to coarse-grained biotite-hornblende tonalite, quartz diorite, and minor diorite. In addition to abundant mafic inclusions, Alpine rocks contain 2- to 3-cm-long concentrations of mafic minerals. Microscopically, these dark concentrations consist of intergrown, partly recrystallized mafic minerals. One- to 2-cm poikilitic biotite and/or hornblende grains are commonly present. As a result of variably sized mafic constituents, the tonalite of Alpine tends to be heterogeneous in outcrop and hand sample. Foliation is well developed due to parallel alignment of (l) magmatic pheno- crysts, (2) recrystallized minerals (subsolidus recrystallization), and (3) mafic aggregates and inclusions. The tonalite of Alpine consists of plagioclase, quartz, subequal hornblende and biotite, and pyroxene. Rarely, rocks contain interstitial K-feldspar, in a few cases enough to produce borderline granodiorite/tonalite compositions. In the Ramona quadrangle, the tonalite of Alpine 1) forms the south- ern end of a pluton in the north-central part of the quadrangle, 2) interfingers with, and grades into the Japatul Valley Tonalite in the northwest quarter, and 3) has a sharp contact with the Kjv unit in the south- east corner of the quadrangle. Progressively less mafic compositions of these two tonalite units, abun- dant mafic inclusions in both, hornblende and biotite as chief mafic minerals, gradational contacts, and similar geochemical characteristics indicate that the Alpine and Japatul Valley units are genetically related. Todd and others (2003) proposed that both units fractionated from a single mafic parental magma. Uranium-lead zircon analysis of a sample from the Alpine type locality yielded an age of 108±2 Ma (D.L. Kimbrough, oral commun., 1992). A conventional K-Ar hornblende cooling age of 107 Ma was obtained for tonalite collected near this site; other K-Ar hornblende ages for the Alpine unit range from 102 to 97 Ma. Ka-w – deeply weatherd Ka. Japatul Valley Tonalite (Cretaceous) - Consists of biotite-hornblende tonalite, hornblende-biotite tonalite, and borderline tonalite/granodiorite that grades to granodiorite. Japatul Valley rocks are medium- to coarse- grained, equigranular, and moderately to strongly foliated. Weathered color ranges from light-gray to grayish-white, and the abundant mafic inclusions commonly weather out in relief. The Japatul Valley unit is composed of plagioclase, quartz, biotite, hornblende, and K-feldspar. Plagioclase of tonalite samples is zoned from labradorite cores to sodic oligoclase rims, and in granodiorite, from sodic andesine to sodic oligoclase. Plagioclase has undergone variable degrees of subsolidus strain and recrystallization. Slightly to moderately strained rocks display subhedral, 4 mm- to 1 cm-long phenocrysts with euhedral oscillatory zoning whose margins are irregular due to replacement and embayment by quartz; grain cores contain small solid-state inclusions of biotite, hornblende, epidote, and white mica. Roughly one-half of Japatul Valley samples are strongly foliated, and in these rocks, plagioclase igneous shapes and zoning are almost obliterated. In mylonitic gneiss, plagioclase occurs as porphyroclasts containing solid-state inclusions of hornblende, biotite, epidote, and quartz, and in recrystallized folia. The Japatul Valley Tonalite underlies a large part of the Ramona quadrangle including its prominent position in the Ramona ring-dike structure and in large areas of San Vicente and Santa Maria Valleys. In the southern part of the map area, the tonalite contains Kmv inclusions and is cut by numerous dikes of the Corte Madera Monzo- granite (Kcm), many of which are too small to show at map scale. This area is part of the northern outermost zone of the El Cajon Mountain plutonic complex to the south, in which Kcm dikes that fringe a central Corte Madera pluton intrude Kmv screens and Kjv tonalite (Todd, 2004). The Kjv unit has not been dated by U-Pb method. South of the Ramona quadrangle, conventional K-Ar hornblende ages of six samples range from 109 to 94 Ma, and 40Ar/39Ar minimum emplacement ages of 112 and 104 Ma were also determined. Las Bancas Tonalite and Japatul Valley Tonalite, gradational unit (Cretaceous) - In the Ramona quadrangle, the Las Bancas Tonalite comprises the central pluton of Merriam’s (1946) ring-dike structure. At two locations along the contact between Klb and the surrounding Japatul Valley Tonalite (Kjv), the two units are separated by a zone of contact breccia that suggests mingling of coeval magmas. In section 7, T.13S., R.2E. a zone between the two plutons up to 700 m wide is composed of rounded blobs of very fine-grained, porphyritic Klb (quenched magma) in a matrix of mafic (contaminated) Japatul Valley Tonal- ite. The implication is that two magma bodies mingled along their contact: high-temperature, fluid Las Bancas magma and a Japatul Valley crystal mush. The Las Bancas-Japatul Valley contact on the east side of Sutherland Lake is characterized by a narrow (~150 m) zone in which very fine-grained, porphy- ritic Las Bancas dikes cut Japatul Valley Tonalite producing a breccia. Las Bancas Tonalite (Cretaceous) - Homogeneous, mafic inclusion-free hypersthene-biotite tonalite with lesser quartz diorite, granodiorite, diorite, and quartz norite. Locally, Las Bancas tonalite is interlayered at outcrop scale with gabbro. On fresh surfaces of average Klb, mafic minerals show through clear, glassy plagioclase grains giving the rock a dark-gray to black color. The unit weathers to large subrounded residual boulders with a reddish-gray to tan color. The Las Bancas rock is typically medium-grained, equigranular, and generally lacks the recrystallized mafic aggregates that charactertize the Alpine and Japatul Valley units. The Klb tonalite has a steep foliation due to the preferred alignment of mineral grains. Plagioclase and mafic minerals of Klb plutons retain euhedral/subhedral grain shapes except near pluton margins where protoclastic textures may be developed. Scattered large (0.5- to 2.5-cm) poikilitic biotite grains (oikocrysts) that enclose early crystallized minerals and appear as reflective cleav- ages on weathered rock faces are characteristic of the unit. Plagioclase (labradorite to sodic andesine) is the most abundant modal mineral. Although locally recrystallized, the largest plagioclase grains (up to 6 mm long) commonly retain delicate euhedral oscillatory zoning. In the most mafic Las Bancas rocks, which contain abundant hypersthene and less than 10% quartz, plagioclase is labradorite to bytownite. This mafic rock may contain indistinct, 2-cm-thick planar concentrations of felsic and mafic minerals oriented parallel to mineral foliation (cumulate layering). The layered rocks also contain pale-weathering lenticular basaltic inclusions as long as 10 cm. In the El Cajon 1:100,000 quadrangle, contacts between the Las Bancas Tonalite and other Cretaceous tonalite units suggest that emplacement ages overlapped. Locally, the Klb unit 1) has a fine-grained margin against the Cuyamaca Gabbro, or contacts may suggest mingling of coeval magmas, and 2) grades to, interfingers with, occurs as inclusions within, and sends dikes of fine-grained pyroxene granodiorite into, the tonalite of Alpine. The Las Bancas-type pluton south of the town of Mount Laguna has an U-Pb zircon age of 104 Ma (L.T. Silver, oral commun., 1979) and the pluton south of the town of Descanso (unit type locality) has an age of 109±2 Ma (D.L. Kimbrough, oral commun., 1992). Conventional K-Ar hornblende cooling ages of 107, 101, and 96 Ma were determined for the Las Bancas unit. Klb-w – deeply weatherd Klb. Western metavolcanic rocks (Cretaceous) - In the southern part of the Ramona quadrangle, several small hills are underlain by metamorphosed silicic and intermediate volcanic rocks that are intruded and surrounded by the Japatul Valley Tonalite. Minor pelitic schist, feldspathic metaquartzite, and plutonic-cobble meta- conglomerate are interlayered with tuff, tuff-breccia, and flows of andesitic, rhyolitic, and basaltic composi- tion. Assigned by most workers on the basis of lithology to the Early Cretaceous-Late Jurassic Santiago Peak Volcanics. These rocks were metamorphosed to amphibolite facies. These outcrops are spatially continuous with similar rocks mapped as Kmv in the El Cajon 1:100,000 quadrangle to the south where tonalite magma apparently assimilated marginal parts of the metavolcanic inclusions producing a variety of hybrid migmatites. Cuyamaca Reservoir Granodiorite (Jurassic) - Fine- to medium-grained and light- to dark-gray on fresh surfaces. Outcrops weather to a distinctive orange-tan color. Consists of subequal biotite and hypersthene-biotite granodiorite and tonalite; many samples have borderline granodiorite/tonalite compo- sitions. Both tonalite and granodiorite compositions can contain actinolitic amphibole. Abundant biotite is present in scaly aggregates and folia made up of recrystallized grains; 1- to 3-mm anhedral or skeletal grains may be relict phenocrysts. The mineral is pleochroic from pale-gold and pale-reddish-orange to dark red-brown. Subhedral (magmatic) hypersthene grains have reaction rims of clinopyroxene and/or biotite. Skeletal pyroxenes may be rimmed and partly replaced by pale-green to colorless actinolite in habits that indicate both magmatic and metamorphic crystallization of actinolite. Abundant sphene is characteristic, occurring as subhedral grains; secondary rims on ilmenite grains; and tiny seed- and wedge-shaped grains located along biotite cleavage planes and in aggregates of recrystallized mafic minerals. Other accessories include apatite, ilmenite, zircon, and allanite. Euhedral /subhedral zircon of the Jcr unit is clear in color, but a few grains contain rounded tan cores. Cuyamaca Reservoir unit is exposed in the southeast part of Ramona quadrangle. Elsewhere in the PRB, plutons of the Jcr unit have yielded Middle and Late Jurassic U-Pb zircon ages (Shaw and others, 2003). Jcr-w – deeply weatherd Jcr. Metavolcanic and metasedimentary rocks (Creataceous - Jurassic) - Exposures occur in four screens in the eastern half of the Ramona quadrangle. These include: two screens north of Sutherland Lake in the northern part of the quadrangle; a third screen north of Mt. Gower in the southern part of the quadrangle; and a fourth in the southeast corner of the quadrangle. The screen north of Mt. Gower consists chiefly of metasedimentary rocks including feldspathic quartzite and mica schist, interlayered with as much as 50% orthoamphibolite. Relict plagioclase phenocrysts indicate the igneous origin of the amphibolites. Mica schist displays compositional banding. Feldspathic quartzite is massive and forms layers 2-10 cm thick separated by fine laminations of mica schist. Graded bedding was observed in some quartzites (Foster, 1994). Feldspathic quartzites have approximately 60% quartz, 30% plagioclase, and variable amounts of hornblende, clinopyroxene, and opaque minerals. Mica schist consists of layers of variable thickness composed of biotite and muscovite with subordinate hornblende and diopside in a matrix of recrystallized quartz and plagioclase. The screen north of Mt. Gower may be in intrusive and/or tectonic contact with the Jurassic Cuyamaca Reservoir unit. At the time of publication, age relations between KJvs and Jcr in the Ramona quadrangle are not resolved. The two northern KJvs screens have not been studied in detail. They are separated by a thin sheet of the tonalite of Alpine (Ka) that is very fine-grained (chilled) against the screens so that the dark-gray to black tonalite superficially resembles fine-grained gabbro. The rocks of the northern screens are less pelitic and possibly more volcanic/volcaniclastic in character than the southern screens. Feldspathic quartzite predominates, both massive and with compositional banding that suggests a tuffaceous protolith. Mica schists are less abundant. At least part of the screen near Suther- land Dam may be tectonic breccia consisting of quartzitic clasts up to 1 meter in diameter. The southern- most KJvs screen in the Ramona quadrangle consists largely of amphibolite and fine-grained gabbro. Qols af Qw QTf Tp Qya Qoa Qoc Kcm Kcp Klp Klp-w Klpm Klpm-w Kc Kjv-w Kjv Kmv Kmv Klb/Kjv KJvs Ka Ka-w Klb Klb-w Jcr Jcr-w DESCRIPTION OF MAP UNITS GN MN 13° 231 MILS 0°06' 2 MILS UTM GRID AND 1988 MAGNETIC NORTH DECLINATION AT CENTER OF SHEET 0 0 0 1 1 1 .5 .5 2 2 2 Thousand Feet Kilometers Miles Contour Interval 20 Feet National Geodetic Vertical Datum of 1929 Scale 1:24,000 Topographic base from U.S. Geological Survey Ramona 7.5-minute Quadrangle, 1988 UTM projection, North American Datum 1927 CALIFORNIA GEOLOGICAL SURVEY JOHN G. PARRISH, Ph.D., STATE GEOLOGIST STATE OF CALIFORNIA - ARNOLD SCHWARZENEGGER, GOVERNOR THE RESOURCES AGENCY - MIKE CHRISMAN, SECRETARY FOR RESOURCES DEPARTMENT OF CONSERVATION - BRIDGETT LUTHER, DIRECTOR Prepared in cooperation with the U.S. Geological Survey, Southern California Areal Mapping Project 116°45'00" 33°07'30" 116°52'30" 33°07'30" 116°52'30" 33°00'00" This geologic map was funded in part by the U.S. Geological Survey National Cooperative Geologic Mapping Program, STATEMAP Award no. 05HQAG0080 116°45'00" 33°00'00" GEOLOGIC MAP OF THE RAMONA 7.5' QUADRANGLE SAN DIEGO COUNTY, CALIFORNIA: A DIGITAL DATABASE Version 1.1 By Victoria R. Todd 1 , Lawrence L. Busch 2 , Brent D. Foster 2 , Janis L. Hernandez 2 , and Siang S. Tan 2 2006 (Revised 2007) Digital Preparation by Carlos I. Gutierrez 2 and Karen Toman-Sager 2 1. U. S. Geological Survey (retired), 1740 Clarion Drive, Williamsport, PA 17701 2. California Geological Survey Copyright © 2006 by the California Department of Conservation California Geological Survey. All rights reserved. No part of this publication may be reproduced without written consent of the California Geological Survey. "The Department of Conservation makes no warranties as to the suitability of this product for any given purpose." CGS CGS S G S AMP S U C Preliminary Geologic Map available from: http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm
Transcript of GEOLOGIC MAP OF THE SAN DIEGO COUNTY, CALIFORNIA: A ... · 5 7 6 65 88 77 68 73 52 86 63 73 81 87...
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References:The bedrock geology is partly modified from Merriam (1953).
Abbott, P.L., and Smith, T.E., 1989, Sonora, Mexico, source for the Eocene Poway Conglomerate of southern California: Geology, v. 17, p. 329-332.
Anderson, C.L., 1991, Zircon uranium-lead isotopic ages of the Santiago Peak Volcanics and spatially related plutons of the Peninsular Ranges batholith, southern California: San Diego State University, M.S. thesis, 111 p.
Bellemen, G.J., and Merriam, R.H., 1958, Petrology and origin of the Poway Conglomerate, San Diego County, California: Geological Society of America Bulletin v. 69, no. 2, p. 199-220. Fig. 1, scale approximately 1:312,500.
Everhart, D.L., 1951, Geology of the Cuyamaca Peak quadrangle, San Diego County, California: California Division of Mines Bulletin 159, p. 51-115.
Foster, B.D., 1994, Origin and tectonic significance of Peninsular Ranges amphibolites: San Diego State University, M.S. thesis, 112 p.
Gastil, G., and Bushee, J., 1961, Geology and geomorphology of eastern San Diego County, Field Trip No. 1, Road Log: Geological Society of America, Field Trip Guidebook, San Diego County, 57th Annual Meeting, San Diego State College, p. 13, geologic map no. 2.
Kennedy, M.P., and Peterson, G.L., 1975, Geology of the San Diego metropolitan area, California; Section B, eastern San Diego metropolitan area: California Division of Mines and Geology Bulletin 200, p. 43-56, scale 1:24,000.
Krummenacher, D., Gastil, R.G., Bushee, J., and Doupont, J., 1975, K-Ar apparent ages, Peninsula Ranges batholith, southern California and Baja California: Geological Society of America Bulletin, v. 86, p. 760-768.
Larsen, E.S., 1948, Batholithic and associated rocks of Corona, Elsinore, and San Luis Rey quadrangles, southern California: Geological Society of America Memoir 29, 182 p.
Merriam, R.H., 1941, A southern California ring-dike: American Journal of Science, v. 239, no. 5, p. 365-371.
Merriam, R.H., 1946, Igneous and metamorphic rocks of the southwestern part of the Ramona (30') quadrangle, San Diego County, California: Geological Society of America Bulletin, vol. 57, no. 3, p. 233-260, pl. 1, scale 1:160:000. Later revisions by R.H. Merriam, 1954, in Geology of southern California: California Division of Mines and Geology Bulletin 170, Geologic Guide no. 5, map no. 10, scale 1:203,000 and R.H. Merriam, unpublished mapping in the Ramona quadrangle, 1951-1953.
Merriam, R.H., 1948, Orbicular structures in aplite dikes near Ramona, California: American Journal of Science, v. 246, no. 3, p. 129-137, fig. 2, scale 1:20,000.
Merriam, R.H., 1954, A typical portion of the southern California batholith, San Diego County, in Geology of southern California: California Division of Mines and Geology Bulletin 170, map sheet no. 22, scale 1:62,500.
Merriam, R.H., 1958, Geology of the Santa Ysabel quadrangle, San Diego County: California Division of Mines and Geology Bulletin 177, pl. 1, scale 1:62,500.
Miller, W.J., 1935, Geomorphology of the southern Peninsular Ranges of California: Bulletin of the Geological Society of America, v. 46, p. 1535-1562.
Miller, F.S., 1937, Petrology of the San Marcos gabbro, southern California: Bulletin of the Geological Society of America, v. 48, no. 10, p. 1397-1426.
Minch, J.A., 1972, The late Mesozoic-early Tertiary framework of continental sedimentation, northern Peninsular Ranges, Baja California, Mexico: University of California, Riverside, Ph.D. dissertation, 192 p.
Ortega-Rivera, Amabel, 2003, Geochronological constraints on the history of the Peninsular Ranges batholith of Alta and Baja California; tectonic implications for western Mexico, in Johnson, S.E., Paterson, S.R., Fletcher, J.M., Girty, G.H., Kimbrough, D.L., and Martin-Barajas, A., editors, Tectonic evolution of northwestern Mexico and the southwestern USA: Geological Society of America Special Paper 374, p. 297-335.
Simpson, D.R., 1965, Geology of the central part of the Ramona pegmatite district, San Diego County, California: California Division of Mines and Geology, Special Report 86, p. 3-23, (a) figure 1, scale 1:60,000, (b) figure 2, scale 1:9,000, (c) figure 4, scale 1:275, (d) figure 5, scale 1:150.
Snee, L.W., Naeser, C.W., Naeser, N.D., Todd, V.R., and Morton, D.M., 1994, Preliminary 40Ar/39Ar and fission-track cooling ages of plutonic rocks across the Peninsular Ranges batholiths, southern California: Geological Society of America Abstracts with Programs, v. 26, no 2, p. 94.
Steer, B.L., and Abbott, P.L., 1984, Paleohydrology of the Eocene Ballena Gravels, San Diego Country, California: Sedimentary Geology, v. 38, p. 181-216.
Streckeisen, A.L., 1973, Plutonic rocks – Classification and nomenclature recommended by the IUGS Subcommission on Systematics of Igneous Rocks: Geotimes, v. 18, p. 26-30
Streckeisen, A.L., 1976, To each plutonic rock a proper name: Earth Science Reviews, v. 12, p. 1-33.
Tan, S.S., 2002, Geologic map of the San Vicente Reservoir 7.5' quadrangle, San Diego County, California: A digital database: California Geological Survey Preliminary Geologic Map website, http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm, scale 1:24,000.
Todd, V.R., 1977, Geologic map of the Cuyamaca Peak quadrangle, San Diego County, California: U.S. Geological Survey Open-File Report 77-405, 13 p., scale 1:24,000.
Todd, V.R., 1983, Geologic map of the El Cajon Mountain quadrangle, San Diego County, California: U.S. Geological Survey Open-File Report 83-781, scale 1:24,000.
Todd, V.R., and Shaw, S.E., 1985, S-type granitoids and an I-S line in the Peninsular Ranges batholith, southern California: Geology, v. 13, no. 4, p. 231-233.
Todd, V.R., Shaw, S.E., and Hammarstrom, J.M., 2003, Cretaceous plutons of the Peninsular Ranges batholith, San Diego and westernmost Imperial counties, California: Intrusion across a Late Jurassic continental margin, in Johnson, S.E., Paterson, S.R., Fletcher, J.M., Girty, G.H., Kimbrough, D.L., and Martin-Barajas, A., editors, Tectonic evolution of northwestern Mexico and the southwestern USA: Geological Society of America Special Paper 374, p. 185-235.
Todd, V.R., 2004, Preliminary geologic map of the El Cajon 30’ x 60’ quadrangle, Southern California: U.S. Geological Survey Open-File Report 2004-1361, 30 p., 2 plates, scale 1:100,000.
Weber, F.H., JR., 1963, Geology and mineral resources of San Diego County, California: California Division of Mines and Geology County Report 3, 309 p.
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Radec Oasis
Rincon
Ramona
Banner
Borrego
Aguanga
Rosemont
Oak Grove
San Ysidro
San Felipe
Pine Hills
SanPasqual
Mesa Grande
SantaYsabel
WarnerSprings
Holcomb Village
Borrego Springs
PalomarMountain
Vail Lake
Aguanga
Beauty Mtn.
BucksnortMtn.
CollinsValley
Boucher Hill
Palomar
Observatory
Warner
Springs
Hot SpringsMtn.
Borrego Palm
Canyon
TubbCanyon
Ranchita
Warners
Ranch
MesaGrande
RodriguezMtn.
San Pasqual
Ramona
SantaYsabel
Julian
Earthquake
Valley
Clark LakeNE
BorregoSink
Clark Lake
Rabbit Peak
Oasis
Mapping completed under STATEMAP
FY 2005-06
FY 2004-05
FY 2002-03
CGS OFR 96-06& CD 2000-08*
*GIS data for the Tubb Canyon 7.5’ quadrangle available on CD - CGS CD 2000-08. Paper copy available as OFR 96-06.
5Kilometers
5 Miles
QuartzSyenite
QuartzMonzonite
QuartzMonzodiorite
Syenite Monzonite Monzodiorite
Alka
li-feld
spar
Gra
nite
Tonalite
Diorite
Gabbro
Syen
ogra
nite
Granodiorite
Mon
zogr
anite
Quartz
Diorite
90 65 35 10
5
20
60Q Q
A P
60
20
5
60
Granite
Classification of plutonic rock types (from Streckeisen, 1973; 1976).A, alkali feldspar; P, plagioclase feldspar; Q, quartz.
CORRELATION OF MAP UNITS
Kc
af
QUATERNARY
Pliocene
Eocene
Paleocene
Holocene
Pleistocene
TERTIARY
CENOZOIC
MESOZOICCRETACEOUS
JURASSIC
Qw
KmvKmvKmvKmvKmvKmvKmvKmvKmvKmv
KmvKmvKmvKmvKmvKmvKmvKmvKmvKcm
KmvKmvKmvKmvKlb/Kjv
KJvs
Qya
KlbKlb-w
KaKa-w
KjvKjv-w
KjvKjv-w
JcrJcr-w
Klp-wKlp Klpm
Klpm-w
Qoc QoaQolsQols
QTf
Tp
Strike and dip of sedimentary beds.25
MAP SYMBOLS
25 Strike and dip of igneous foliation.
Vertical igneous foliation.
25 Strike and dip of metamorphic foliation.
Vertical metamorphic foliation.
Contact between map units - Solid where accurately located, dashed where approximately located; dotted where conselaed; queried where existence is questionable.Fault - Dashed where approximately located; dotted where concealed.
? Landslide - arrow indicates principal direction of movement, queried where existence is questionable.
Pegmatite dike of the Ramona pegmatite district.
?
Aplite dike.
Leucocratic dike; related to Klp.
Leucocratic dike; related to Kcm.
Artificial fill (late Holocene) - Includes concrete dam structure at Sutherland Lake, and mixtures of non-engineered fill consisting of sand, gravel, trash and debris at the Ramona Landfill.
Wash deposits (late Holocene) - Unconsolidated sand and gravel deposited in active washes. Consists of light brownish-gray (2.5Y 6/2) to grayish-brown (10YR 5/2), fine- to medium-grained sand, silt, and coarse sand to fine gravel. Sand is angular to sub-angular, micaceous, and is primarily derived from local bedrock. Subject to localized reworking and new sediment deposition during winter storms.
Young axial channel deposits (Holocene to late Pleistocene) - Unconsolidated to slightly consolidated sand and gravel deposited in marginal parts of active washes. Consists of grayish-brown (2.5Y 5/2) to dark grayish-brown (10YR 4/2), fluvial deposits of fine- to coarse-grained sand with minor silt, and minor fine to coarse gravel and cobbles. Gravel and cobbles are sub-rounded to rounded. In most areas, unit is slightly elevated above the active younger wash deposits.
Old colluvial deposits (Late to middle Pleistocene) - Unconsolidated to well consolidated deposits of sediment, rock fragments and soil material deposited by creep and rainwash. Consists of brown (7.5YR 4/3) to (7.5YR 5/4), fine- to coarse-grained sand, clay, silt, and minor fine gravel. Mapped where thick enough to obscure underlying bedrock. Forms aprons along the base of slopes.
Old alluvium (Late to middle Pleistocene) - Moderately consolidated silt, sand and gravel deposited in older fluvial system. Consists of thin- to medium-bedded sandstone and minor conglomerate. Occurs as moderately to highly dissected terraces above stream valleys and in highland valley canyons.
Older landslide deposits (Pleistocene) - Slope-failure deposits consisting of poorly to moderately consolidated, poorly sorted rock fragments and soil material. May be susceptible to renewed slope movements.
Fanglomerate (Quaternary or Tertiary(?)) - Moderately to well-indurated, massively bedded, poorly sorted to unsorted, micaceous, silty, fine- to medium-grained, brown (10YR5/3) arkosic sandstone. Matrix-supported angular (0.5 to 3 cm) clasts of locally derived pegmatitic rock common. Near its base, the deposit contains abundant clasts of angular pegmatitic material as much as 20 cm in maximum dimen-sion; rare broken Poway-type metavolcanic and quartzite cobble clasts up to 7 cm; and rounded, “rotten” granitic boulders. Boulders average 30 cm in diameter and exceed one meter in maximum dimension. Fossiliferous; fossils consist of root casts and other unidentified casts and debris. Occurs as debris flow and fan deposits at base of slopes and in small drainages. Poorly exposed, usually only observed in roadcuts and gullies. Desiccation cracks common. Queried Tertiary age assignment based on degree of induration, and stratigraphic position above crystalline basement and below deeply weathered, eroded, unindurated colluvium. May include deposits related to Ballena River system.
Poway Group/Ballena Gravels (Eocene-Paleocene) - Remnant fluvial-channel deposits of the Ballena River system. Massively bedded conglomerates, conglomeratic sandstone, and minor beds and lenses of sandstone up to 300 feet thick. Predominantly well-rounded to subrounded, resistant, exotic “Poway-type” metavolcanic and quartzite clasts with minor amounts of weathered clasts of locally derived crystal-line basement in a well-consolidated sandy matrix. Poway-type clasts characteristically are gray to red, weakly metamorphosed, porphyritic rhyolite and dacite with feldspar and quartz phenocrysts. Maximum long-dimension of clasts in the Ramona quadrangle approaches three feet. Auriferous.
Tonalite of La Posta (Cretaceous) - Rocks tentatively correlated with La Posta-type plutons of the eastern zone of the PRB. Consists of homogeneous, idiomorphic medium- to coarse-grained hornblende-biotite tonalite, trondhjemite (leucotonalite), and leucogranodiorite. The unit is in part equivalent to the La Posta Quartz Diorite of Miller (1935). La Posta rocks contain abundant white-weathering plagioclase and low color index (C.I.), which together impart a white color to the low platy outcrops of the unit. Also character-istic are: 1) light-gray quartz grains up to 1 cm+ of bipyramidal to ovoid shape, 2) euhedral, barrel-shaped biotite books (0.5- to 1-cm across by 1.5 cm in length), and 3) scattered 2- to 5-cm-long K-feldspar oikocrysts that appear as glassy reflective cleavages on weathered rock surfaces. Grains of pale-yellow euhedral sphene are commonly visible in hand sample. The La Posta unit consists of plagioclase, quartz, biotite ± hornblende ± K-feldspar; in granodiorite and monzogranite, K-feldspar equals or exceeds biotite. In the Ramona quadrangle, the tonalite of La Posta forms an outer pluton of the Ramona ring-dike structure located along the structure’s southern and western sides. Medium-grained leucotonalite and tonalite/granodiorite of this pluton display idiomorphic texture (due to hornblende and biotite phenocrysts), are quartz-rich, and contain K-feldspar oikocrysts and visible sphene. A small exposure in the northwest corner of the quadrangle is also underlain by Klp. The larger Klp pluton in the Ramona quadrangle is petrographically similar to the La Posta-type pluton south of the town of Alpine, which is the westernmost exposure of the unit in the El Cajon 1:100,000 quadrangle. The Klp pluton of the Ramona ring-dike structure appears to be the origin of numerous large pegmatite dikes that intrude the quadrangle’s northwest quarter. Klp-w – deeply weatherd Klp.
Tonalite of La Posta, Mafic phase (Cretaceous) – Rocks that partially border the tonalite of La Posta in the Ramona quadrangle. The rocks assigned to the mafic phase of La Posta are mineralogically and textur-ally similar to La Posta rocks but are more mafic. Unit consists of light-gray-weathering, strongly foliated, fine- to medium-grained tonalite that is less resistant to erosion and therefore crops out less prominently than La Posta. Tonalite of the mafic phase contains subequal biotite and hornblende as single euhedral/subhedral phenocrysts (idiomorphic texture), abundant quartz, euhedral sphene, scarce K-feldspar oikocrysts, and few mafic inclusions. At one locality, the La Posta pluton contains an inclusion of the mafic phase near its margin. Rocks assigned to the mafic phase of La Posta are tentatively corre-lated with the informally named tonalite of Granite Mountain (Kgm; Todd, 1979), which composes large zoned plutons in the eastern zone of the PRB and also occurs as envelopes of varying size surrounding small La Posta-type plutons in the western zone (Todd, 2004). South of the Ramona quadrangle, the Granite Mountain unit has isotopic ages of 98 ± 3 Ma (L.T. Silver, oral commun., 1979) and 101 ± 2 Ma (D.L. Kimbrough, oral commun., 1992). These ages are slightly older than those of adjacent La Posta plutons. Klpm-w – deeply weatherd Klpm.
Cuyamaca Gabbro (Cretaceous) - The Cuyamaca Gabbro (Everhart, 1951) is the name given to large gabbro plutons, smaller gabbro bodies, and gabbroic dikes in central and southern San Diego County. Most of the gabbro in the Ramona quadrangle occurs in small bodies and dikes within granitic rocks. These rocks are fine- to coarse-grained and dark colored on fresh surfaces but typically weather to form a reddish soil with sparse outcrop. Textures are magmatic with slight recrystallization. Although some outcrops appear massive, most are foliated to some extent. Some display a strong foliation due to recrystallized mafic minerals. Flow banding is present near contact zones. Most gabbros have abundant fine-grained anhedral orthopyroxene with scarce subhedral phenocrysts. Hornblende is poikilitic and interstitial. Plagioclase typically occurs as subhedral laths. Abundant opaque oxide occurs as disseminated intersti-tial grains and as inclusions in hornblende and plagioclase. Some rocks have larger subhedral grains of hornblende with cores that appear to be altered pyroxene. A more leucocratic variety of gabbro occurs either interlayered with or gradational to the more common mafic variety. This rock has less abundant mafic minerals and may have fine-grained interstitial quartz. Gabbro assigned to the Cuyamaca Gabbro (Kc) is present in a discontinuous series of small pod-like bodies that are part of the Ramona ring-dike structure. Conventional K-Ar analysis of hornblende from two gabbro plutons south of the Ramona quadrangle yielded cooling ages of 108 and 104 Ma. An U-Pb zircon age of 107± 2 Ma for the gabbro pluton that underlies Poser Mountain in the Viejas Mountain 7.5-minute quadrangle is essentially the same as the age of the Ka pluton at the latter’s nearby type locality (D. L. Kimbrough, oral commun., 1992).
Corte Madera Monzogranite (Cretaceous) - Corte Madera rocks consist of medium- to coarse-grained biotite leucomonzogranite, leucogranodiorite, and syenogranite as well as abundant dikes of leucogranite, alaskite, pegmatite, and aplite. Outcrops of the unit weather white with a pinkish-orange (peach) hue. Scarce mafic grains in Corte Madera rocks form lenticular aggregates whose wide (0.5-2 cm) spacing imparts a distinctive spotted appearance to rock surfaces. Foliation fabrics in Kcm rocks range from weak magmatic to strong synmagmatic or post-magmatic (subsolidus). Monzogranite of the Kcm unit is com-posed of subequal quartz and plagioclase with lesser K-feldspar and biotite; about half of petrographic samples contain small relict hornblendes. Granodiorite consists of plagioclase, quartz, K-feldspar, and biotite. Major minerals of the syenogranite phase of the Kcm unit are K-feldspar, quartz, plagioclase, and biotite. Characteristically, quartz in all facies of the unit occurs as subequant to lenticular grains as long as 1 cm; in moderately strained rocks, quartz phenocrysts are partly recrystallized to subgrains, whereas in highly strained rocks, quartz occurs in lenticular multi-grain aggregates and ribbons >1 centimeter long. Corte Madera plutons typically comprise the most centrally located and latest intrusions in Cretaceous zoned plutonic complexes in the western zone of the PRB (Todd and others, 2003). In the southern part of the Ramona quadrangle, Kcm forms the Mt. Gower pluton and its fringing dikes and also occurs as small bodies and dikes in the Japatul Valley Tonalite. An U-Pb zircon age of 111± 2 Ma was reported for the central Corte Madera-type pluton that underlies El Cajon Mountain (D.L. Kimbrough, oral commun., 1992). Conventional K-Ar hornblende cooling ages of 105 and 102 Ma were determined for two addi-tional plutons of the unit.
Tonalite of Alpine (Cretaceous) - Consists of medium- to coarse-grained biotite-hornblende tonalite, quartz diorite, and minor diorite. In addition to abundant mafic inclusions, Alpine rocks contain 2- to 3-cm-long concentrations of mafic minerals. Microscopically, these dark concentrations consist of intergrown, partly recrystallized mafic minerals. One- to 2-cm poikilitic biotite and/or hornblende grains are commonly present. As a result of variably sized mafic constituents, the tonalite of Alpine tends to be heterogeneous in outcrop and hand sample. Foliation is well developed due to parallel alignment of (l) magmatic pheno-crysts, (2) recrystallized minerals (subsolidus recrystallization), and (3) mafic aggregates and inclusions. The tonalite of Alpine consists of plagioclase, quartz, subequal hornblende and biotite, and pyroxene. Rarely, rocks contain interstitial K-feldspar, in a few cases enough to produce borderline granodiorite/tonalite compositions. In the Ramona quadrangle, the tonalite of Alpine 1) forms the south-ern end of a pluton in the north-central part of the quadrangle, 2) interfingers with, and grades into the Japatul Valley Tonalite in the northwest quarter, and 3) has a sharp contact with the Kjv unit in the south-east corner of the quadrangle. Progressively less mafic compositions of these two tonalite units, abun-dant mafic inclusions in both, hornblende and biotite as chief mafic minerals, gradational contacts, and similar geochemical characteristics indicate that the Alpine and Japatul Valley units are genetically related. Todd and others (2003) proposed that both units fractionated from a single mafic parental magma. Uranium-lead zircon analysis of a sample from the Alpine type locality yielded an age of 108±2 Ma (D.L. Kimbrough, oral commun., 1992). A conventional K-Ar hornblende cooling age of 107 Ma was obtained for tonalite collected near this site; other K-Ar hornblende ages for the Alpine unit range from 102 to 97 Ma. Ka-w – deeply weatherd Ka.
Japatul Valley Tonalite (Cretaceous) - Consists of biotite-hornblende tonalite, hornblende-biotite tonalite, and borderline tonalite/granodiorite that grades to granodiorite. Japatul Valley rocks are medium- to coarse-grained, equigranular, and moderately to strongly foliated. Weathered color ranges from light-gray to grayish-white, and the abundant mafic inclusions commonly weather out in relief. The Japatul Valley unit is composed of plagioclase, quartz, biotite, hornblende, and K-feldspar. Plagioclase of tonalite samples is zoned from labradorite cores to sodic oligoclase rims, and in granodiorite, from sodic andesine to sodic oligoclase. Plagioclase has undergone variable degrees of subsolidus strain and recrystallization. Slightly to moderately strained rocks display subhedral, 4 mm- to 1 cm-long phenocrysts with euhedral oscillatory zoning whose margins are irregular due to replacement and embayment by quartz; grain cores contain small solid-state inclusions of biotite, hornblende, epidote, and white mica. Roughly one-half of Japatul Valley samples are strongly foliated, and in these rocks, plagioclase igneous shapes and zoning are almost obliterated. In mylonitic gneiss, plagioclase occurs as porphyroclasts containing solid-state inclusions of hornblende, biotite, epidote, and quartz, and in recrystallized folia. The Japatul Valley Tonalite underlies a large part of the Ramona quadrangle including its prominent position in the Ramona ring-dike structure and in large areas of San Vicente and Santa Maria Valleys. In the southern part of the map area, the tonalite contains Kmv inclusions and is cut by numerous dikes of the Corte Madera Monzo-granite (Kcm), many of which are too small to show at map scale. This area is part of the northern outermost zone of the El Cajon Mountain plutonic complex to the south, in which Kcm dikes that fringe a central Corte Madera pluton intrude Kmv screens and Kjv tonalite (Todd, 2004). The Kjv unit has not been dated by U-Pb method. South of the Ramona quadrangle, conventional K-Ar hornblende ages of six samples range from 109 to 94 Ma, and 40Ar/39Ar minimum emplacement ages of 112 and 104 Ma were also determined.
Las Bancas Tonalite and Japatul Valley Tonalite, gradational unit (Cretaceous) - In the Ramona quadrangle, the Las Bancas Tonalite comprises the central pluton of Merriam’s (1946) ring-dike structure. At two locations along the contact between Klb and the surrounding Japatul Valley Tonalite (Kjv), the two units are separated by a zone of contact breccia that suggests mingling of coeval magmas. In section 7, T.13S., R.2E. a zone between the two plutons up to 700 m wide is composed of rounded blobs of very fine-grained, porphyritic Klb (quenched magma) in a matrix of mafic (contaminated) Japatul Valley Tonal-ite. The implication is that two magma bodies mingled along their contact: high-temperature, fluid Las Bancas magma and a Japatul Valley crystal mush. The Las Bancas-Japatul Valley contact on the east side of Sutherland Lake is characterized by a narrow (~150 m) zone in which very fine-grained, porphy-ritic Las Bancas dikes cut Japatul Valley Tonalite producing a breccia.
Las Bancas Tonalite (Cretaceous) - Homogeneous, mafic inclusion-free hypersthene-biotite tonalite with lesser quartz diorite, granodiorite, diorite, and quartz norite. Locally, Las Bancas tonalite is interlayered at outcrop scale with gabbro. On fresh surfaces of average Klb, mafic minerals show through clear, glassy plagioclase grains giving the rock a dark-gray to black color. The unit weathers to large subrounded residual boulders with a reddish-gray to tan color. The Las Bancas rock is typically medium-grained, equigranular, and generally lacks the recrystallized mafic aggregates that charactertize the Alpine and Japatul Valley units. The Klb tonalite has a steep foliation due to the preferred alignment of mineral grains. Plagioclase and mafic minerals of Klb plutons retain euhedral/subhedral grain shapes except near pluton margins where protoclastic textures may be developed. Scattered large (0.5- to 2.5-cm) poikilitic biotite grains (oikocrysts) that enclose early crystallized minerals and appear as reflective cleav-ages on weathered rock faces are characteristic of the unit. Plagioclase (labradorite to sodic andesine) is the most abundant modal mineral. Although locally recrystallized, the largest plagioclase grains (up to 6 mm long) commonly retain delicate euhedral oscillatory zoning. In the most mafic Las Bancas rocks, which contain abundant hypersthene and less than 10% quartz, plagioclase is labradorite to bytownite. This mafic rock may contain indistinct, 2-cm-thick planar concentrations of felsic and mafic minerals oriented parallel to mineral foliation (cumulate layering). The layered rocks also contain pale-weathering lenticular basaltic inclusions as long as 10 cm. In the El Cajon 1:100,000 quadrangle, contacts between the Las Bancas Tonalite and other Cretaceous tonalite units suggest that emplacement ages overlapped. Locally, the Klb unit 1) has a fine-grained margin against the Cuyamaca Gabbro, or contacts may suggest mingling of coeval magmas, and 2) grades to, interfingers with, occurs as inclusions within, and sends dikes of fine-grained pyroxene granodiorite into, the tonalite of Alpine. The Las Bancas-type pluton south of the town of Mount Laguna has an U-Pb zircon age of 104 Ma (L.T. Silver, oral commun., 1979) and the pluton south of the town of Descanso (unit type locality) has an age of 109±2 Ma (D.L. Kimbrough, oral commun., 1992). Conventional K-Ar hornblende cooling ages of 107, 101, and 96 Ma were determined for the Las Bancas unit. Klb-w – deeply weatherd Klb.
Western metavolcanic rocks (Cretaceous) - In the southern part of the Ramona quadrangle, several small hills are underlain by metamorphosed silicic and intermediate volcanic rocks that are intruded and surrounded by the Japatul Valley Tonalite. Minor pelitic schist, feldspathic metaquartzite, and plutonic-cobble meta-conglomerate are interlayered with tuff, tuff-breccia, and flows of andesitic, rhyolitic, and basaltic composi-tion. Assigned by most workers on the basis of lithology to the Early Cretaceous-Late Jurassic Santiago Peak Volcanics. These rocks were metamorphosed to amphibolite facies. These outcrops are spatially continuous with similar rocks mapped as Kmv in the El Cajon 1:100,000 quadrangle to the south where tonalite magma apparently assimilated marginal parts of the metavolcanic inclusions producing a variety of hybrid migmatites.
Cuyamaca Reservoir Granodiorite (Jurassic) - Fine- to medium-grained and light- to dark-gray on fresh surfaces. Outcrops weather to a distinctive orange-tan color. Consists of subequal biotite and hypersthene-biotite granodiorite and tonalite; many samples have borderline granodiorite/tonalite compo-sitions. Both tonalite and granodiorite compositions can contain actinolitic amphibole. Abundant biotite is present in scaly aggregates and folia made up of recrystallized grains; 1- to 3-mm anhedral or skeletal grains may be relict phenocrysts. The mineral is pleochroic from pale-gold and pale-reddish-orange to dark red-brown. Subhedral (magmatic) hypersthene grains have reaction rims of clinopyroxene and/or biotite. Skeletal pyroxenes may be rimmed and partly replaced by pale-green to colorless actinolite in habits that indicate both magmatic and metamorphic crystallization of actinolite. Abundant sphene is characteristic, occurring as subhedral grains; secondary rims on ilmenite grains; and tiny seed- and wedge-shaped grains located along biotite cleavage planes and in aggregates of recrystallized mafic minerals. Other accessories include apatite, ilmenite, zircon, and allanite. Euhedral /subhedral zircon of the Jcr unit is clear in color, but a few grains contain rounded tan cores. Cuyamaca Reservoir unit is exposed in the southeast part of Ramona quadrangle. Elsewhere in the PRB, plutons of the Jcr unit have yielded Middle and Late Jurassic U-Pb zircon ages (Shaw and others, 2003). Jcr-w – deeply weatherd Jcr.
Metavolcanic and metasedimentary rocks (Creataceous - Jurassic) - Exposures occur in four screens in the eastern half of the Ramona quadrangle. These include: two screens north of Sutherland Lake in the northern part of the quadrangle; a third screen north of Mt. Gower in the southern part of the quadrangle; and a fourth in the southeast corner of the quadrangle. The screen north of Mt. Gower consists chiefly of metasedimentary rocks including feldspathic quartzite and mica schist, interlayered with as much as 50% orthoamphibolite. Relict plagioclase phenocrysts indicate the igneous origin of the amphibolites. Mica schist displays compositional banding. Feldspathic quartzite is massive and forms layers 2-10 cm thick separated by fine laminations of mica schist. Graded bedding was observed in some quartzites (Foster, 1994). Feldspathic quartzites have approximately 60% quartz, 30% plagioclase, and variable amounts of hornblende, clinopyroxene, and opaque minerals. Mica schist consists of layers of variable thickness composed of biotite and muscovite with subordinate hornblende and diopside in a matrix of recrystallized quartz and plagioclase. The screen north of Mt. Gower may be in intrusive and/or tectonic contact with the Jurassic Cuyamaca Reservoir unit. At the time of publication, age relations between KJvs and Jcr in the Ramona quadrangle are not resolved. The two northern KJvs screens have not been studied in detail. They are separated by a thin sheet of the tonalite of Alpine (Ka) that is very fine-grained (chilled) against the screens so that the dark-gray to black tonalite superficially resembles fine-grained gabbro. The rocks of the northern screens are less pelitic and possibly more volcanic/volcaniclastic in character than the southern screens. Feldspathic quartzite predominates, both massive and with compositional banding that suggests a tuffaceous protolith. Mica schists are less abundant. At least part of the screen near Suther-land Dam may be tectonic breccia consisting of quartzitic clasts up to 1 meter in diameter. The southern-most KJvs screen in the Ramona quadrangle consists largely of amphibolite and fine-grained gabbro.
Qols
af
Qw
QTf
Tp
Qya
Qoa
Qoc
Kcm
KcpKlp
Klp-w
Klpm
Klpm-w
Kc
Kjv-w
Kjv
KmvKmv
Klb/Kjv
KJvs
Ka
Ka-w
Klb
Klb-w
Jcr
Jcr-w
DESCRIPTION OF MAP UNITS
GNMN
13°231 MILS0°06'
2 MILS
UTM GRID AND 1988 MAGNETIC NORTHDECLINATION AT CENTER OF SHEET
0
0
0
1
1
1.5
.5 2
2
2Thousand Feet
Kilometers
Miles
Contour Interval 20 FeetNational Geodetic Vertical Datum of 1929
Scale 1:24,000Topographic base from U.S. Geological SurveyRamona 7.5-minute Quadrangle, 1988UTM projection, North American Datum 1927
CALIFORNIA GEOLOGICAL SURVEYJOHN G. PARRISH, Ph.D., STATE GEOLOGIST
STATE OF CALIFORNIA - ARNOLD SCHWARZENEGGER, GOVERNORTHE RESOURCES AGENCY - MIKE CHRISMAN, SECRETARY FOR RESOURCES
DEPARTMENT OF CONSERVATION - BRIDGETT LUTHER, DIRECTORPrepared in cooperation with the U.S. Geological Survey, Southern California Areal Mapping Project
116°45'00"33°07'30"
116°52'30"33°07'30"
116°52'30"33°00'00"
This geologic map was funded in part by the U.S. Geological Survey National CooperativeGeologic Mapping Program, STATEMAPAward no. 05HQAG0080
116°45'00"33°00'00"
GEOLOGIC MAP OF THE RAMONA 7.5' QUADRANGLE
SAN DIEGO COUNTY, CALIFORNIA: A DIGITAL DATABASEVersion 1.1
ByVictoria R. Todd1, Lawrence L. Busch2, Brent D. Foster2, Janis L. Hernandez2, and Siang S. Tan2
2006(Revised 2007)
Digital Preparation byCarlos I. Gutierrez2 and Karen Toman-Sager2
1. U. S. Geological Survey (retired), 1740 Clarion Drive, Williamsport, PA 177012. California Geological Survey
Copyright © 2006 by the California Department of ConservationCalifornia Geological Survey. All rights reserved. No part ofthis publication may be reproduced without written consent of theCalifornia Geological Survey.
"The Department of Conservation makes no warranties as to thesuitability of this product for any given purpose."
CGSCGSSGSA M PSUC
Preliminary Geologic Map available from:http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm
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