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 develops in northeastern reaches of Slough

Expanding Salt Marsh

Freshwater Events Pollen core from upper Slough – fluctuating pickleweed and sedge

A brackish, quiet-water estuary 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, 1769 Expedition, in search of Monterey, follows Salinas River to coastExpedition, in search of Monterey, follows Salinas River to coast Lost, they continue north, through Elkhorn watershed, to San Francisco BayLost, they continue north, through Elkhorn watershed, to San Francisco Bay Miguel 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 Grants Diseño 1830s

Tembladero Slough Salinas River River Mouth

American Accounts 1850s – 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 or Northfork N Monterey Bay 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 Schwartz Robert Curry Doug Smith John Oliver Peter Slattery Bryan Largay Stanley Stevens Michael Fineman