San Luis National Wildlife Refuge Complex - Grasslands Wildlife Management Area

The Grasslands Wildlife Management Area (GWMA) was established by the U.S. Fish and Wildlife Service in 1979 and is composed of privately owned lands on which perpetual conservation easements have been purchased. These easements preserve wetland and grassland habitats and prevent conversion to croplands or other uses not compatible with migratory bird and other wildlife values. Daily management operations remain under the landowner's control. The majority of easement properties are wetlands managed for waterfowl hunting. From 1979 to-date, over 65,000 acres (260 km2) have been placed under conservation easements.

The GWMA is located in western Merced County, California, within the San Joaquin River basin and supports the largest remaining block of contiguous wetlands in the Central Valley. It is divided into an eastern and western division separated by the San Joaquin River. In the heart of the western division is the Grassland Resource Conservation District (GRCD), an area of 70,000 acres (280 km2) of private wetlands and associated grasslands, and over 30,600 acres (124 km2) of federal National Wildlife Refuges and state Wildlife Management Areas.

These private wetlands constitute 30% of the remaining wetlands in California's Central Valley and are extremely important to Pacific Flyway waterfowl populations. Over 60 million duck use-day and 3 million goose use-days occur annually in the GWMA. The wetlands support diverse habitats including seasonally flooded marshlands, semi-permanent marsh, riparian habitat, wet meadows, vernal pools, native uplands, pastures, and native grasslands. This habitat diversity supports raptors, shorebirds, wading birds, and other wildlife species. Several federal and state listed, endangered, and threatened plants and animals are present in the area and benefit by the habitat protection provided by the easement program.