Elkhorn Slough in the Past:

Evidence from sediment cores and historical records

Glacial Maximum

20,000 years B.P.

Global Sea Level Rise

• 18,000 to 7,000 years B.P. Sea level rises rapidly

• 11,000 – 10,000 years B.P. Sea water invades Elkhorn Valley and Moro Cojo

• 8,000 years B.P. Elkhorn Slough is a high-energy tidal inlet

Evolution of mudflats and salt marsh

• 7,000 years B.P. Sea level rise slows

• Energy level of water decreasing in Elkhorn Slough

• Mudflats and salt marshes begin to develop as sediment deposition equals or exceeds sea level rise

Freshwater marsh Freshwater marsh develops in develops in

northeastern reaches northeastern reaches of Sloughof Slough

Expanding Salt MarshExpanding Salt Marsh

Freshwater Events

Pollen core from upper Slough – fluctuating pickleweed and sedge

A brackish, quiet-water estuary

2000 - 1000 years B.P., sediments at mouth indicate:

– Relatively low energy system – may indicate an indirect opening to the ocean

– Salinity between ~ 5 and 20 ppt

Portola Expedition, 1769Portola Expedition, 1769

•Expedition, in search of Expedition, in search of Monterey, follows Salinas Monterey, follows Salinas River to coastRiver to coast

•Lost, they continue north, Lost, they continue north, through Elkhorn watershed, through Elkhorn watershed, to San Francisco Bayto San Francisco Bay Miguel Costanso, 1770Miguel Costanso, 1770

“The [Salinas] river here . . . empties into this great embayment and along its rim turns into a good-sized estuary reaching about two leagues inland, and causing the river here to rise and fall with the tide. It becomes very full-flowing and deep, down close to the sea, so that it cannot be forded, seemingly being all one very deep pool with a great deal of water in it. It is not very wide, some dozen yards it must be.”

Father Crespi’s Account, 1769: Mulligan Hill

Elkhorn

Salinas River

Monterey Bay, 1853

Mexican Land GrantsMexican Land Grants

Diseño 1830s

Diseño 1830s

Tembladero Slough

Salinas River

River Mouth

American Accounts1850s – 1880s

• 1854 U.S. Coast and Geodetic Survey shows salt marsh, salt ponds, tidal creeks, and tide lines in lower Elkhorn Slough

• 1854: geologist John Trask says that the sloughs near the coast “contain sufficient depth of water to float a medium sized vessel” Mouth of Salinas River and

Elkhorn Slough. USCGS, 1854

U.S Surveyor, A.T. Herrmann, 1879

Salinas River

Moro Cojo or “Castroville”

Elkhorn

Bennett orNorthfork

N

MontereyBay

Dunes

Moss Landing wharf

“The upper end of [the Salinas Valley] rests upon Monterey Bay, and has some worthless salt marsh lands. Running through these tide water marshes, one can see along the indentations of the bay hundreds of solemn-looking pelicans, with bills bowed on their baggy

Views from the train, 1870s

throats, appearing to take a most unfavorable view of affairs generally. As we ran along the inlets of the bay, ducks, gulls and other fowl, in great flocks, took to wing and got away. . .”

Moss Landing, 1919

View from the Train, 1880s

[From Hudson’s Landing] “the course of the railroad. . .is now parallel with the general line of the coast, and crosses the tide-lands that skirt the eastern shore of Monterey Bay””

Railroad 1880

Conclusions

• Elkhorn Slough is part of an regional estuarine network that formed about 10,000 years ago

• These wetlands received variable amounts of tidal and freshwater influence over the last 5000 years – usually functioning as a true estuaries: influenced significantly by tidal waters and freshwater input

• In the past, the Salinas river mouth moved frequently

Conclusions, continued

• Over the past 5000 years, these sloughs were dominated by salt marshes and mudflats flanking channels; their upper margins of harbored brackish or freshwater marshes

• Like many others on this coast, the estuarine system was depositional, gradually filling in, with mudflats and channels getting narrower and salt marshes expanding

The Pajaronian 1868

Thanks to:

David SchwartzRobert CurryDoug SmithJohn OliverPeter SlatteryBryan LargayStanley StevensMichael Fineman