Grassland Ecological Area. 02/02/05; California; 65,000 ha; 37°10'N 120°50'W. National Wildlife Refuge, Western Hemisphere Shorebird Reserve. Located in the Central Valley in the San Joaquin River Basin, the site is the largest remaining contiguous block of freshwater wetlands in California. It consists of semipermanent and permanent marshes, riparian corridors, vernal pool complexes, wet meadows, native uplands and grasslands, featuring Alkali Sacaton grassland Sporobolus airoides and the endemic Delta button celery, Eryngium racemosum. The site is renowned for its wintering waterbirds which reach several hundred thousands every winter. These include Sandhill Cranes (Grus canadensis), 19 duck species (Northern pintail Anas acuta; Green-winged teal Anas crecca; Northern shoveler Anas clypeata; Canvasbacks Aythya valisineria and others), 6 species of geese, tens of thousands of shorebirds (most abundantly Western Sandpiper Calidris mauri, Dunlin Calidris alpina and Long-billed dowitcher Limnodromus scolopaceus). The site is home to four endangered shrimps as well the threatened Giant garter snake Thamnophis gigas. Due to flood-control and irrigation projects the entire hydrology of the valley had been dramatically altered, but water quality and allocation issues have been successfully addressed with the Central Valley Project Improvement Act in 1992. Most of the wetlands are managed by the controlled application of water using a series of canals and control structures, mimicking historical flood patterns with pulses of high water flow during winter and spring. The largest potential threat to the site is urban development. Ramsar site no. 1451. Most recent RIS information: 2005.