The complex is an integral part of a mosaic of federal, state, and private lands in Merced and Stanislaus Counties that together constitute the largest contiguous freshwater wetlands remaining in California.
[1] The San Luis National Wildlife Refuge encompasses over 26,600 acres (108 km2) of wetlands, riparian forests, native grasslands and vernal pools.
The refuge is host to significant assemblages of birds, mammals, reptiles, amphibians, insects and plants; some of which, such as the California tiger salamander and San Joaquin kit fox, are endangered species.
The refuge is a major wintering ground and migratory stopover point for large concentrations of waterfowl, shorebirds and other waterbirds.
In these areas, visitors might encounter coyotes, desert cottontails, ground squirrels, western meadowlarks, yellow-billed magpies, loggerhead shrikes, as well as northern harriers and white-tailed kites coursing over the vegetation and other raptors.
The refuge plays host to the largest wintering populations of lesser sandhill cranes and Ross's geese within the Pacific Flyway.
Each autumn over 20,000 cranes and 60,000 arctic-nesting geese terminate their annual migrations from Alaska and Canada to make the refuge home for six months.
The refuge also provides an important breeding habitat for Swainson's hawks, tricolored blackbirds, marsh wrens, mallards, gadwalls, cinnamon teal, and burrowing owls.
The pools come to life as they fill with water: fairy and tadpole shrimp emerge from cysts embedded in the soils the previous year.
The vast number of aquatic invertebrates found in these pools provides a food source for wintering and migrating birds as they prepare for the long flight north to their breeding grounds.
Grazing cattle and sheep is a management tool used by the refuge to help control invasive weeds, provide and maintain short stature grasslands for goose grazing, and encourage native grasslands to thrive[3] The San Joaquin River National Wildlife Refuge is located in Stanislaus County and San Joaquin County.
It encompasses over 7,000 acres (28 km2) of riparian woodlands, wetlands and grasslands that host a diversity of wildlife native to California's Central Valley.
It is estimated that 95 percent of the San Joaquin Valley's riparian woodlands were lost during the late 19th and 20th centuries due to changing land and water uses.
Within the borders of the San Joaquin NWR is one of California's largest riparian forest habitat restoration projects: 400,000 native trees such as willows, cottonwoods, and oaks have been planted across 1,700 acres (7 km2) of river floodplain creating the largest block of contiguous riparian woodland in the San Joaquin Valley.
These woodlands also support a diversity of breeding songbirds including grosbeaks, orioles, flycatchers and warblers, as well as least Bell's vireos – a threatened species which last nested in the San Joaquin Valley over 50 years ago.
These easements preserve wetland and grassland habitats and prevent conversion to croplands or other uses not compatible with migratory birds and other wildlife values.
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.
Several federal and state-listed, endangered, and threatened plants and animals are present in the area and benefit from the habitat protection provided by the easement program.