The San Luis Refuge in the San Joaquin Valley of central California is one of the last remnants of the historically bountiful wintering grounds for migratory waterfowl of the Pacific Flyway. Located in the Bear Creek, Salt Slough, and San Joaquin River floodplain, it hosts a myriad of tree-lined channels and oxbows, wetlands and native grasslands.

Thousands of acres of wetlands, fed by an intricate set of canals, are managed to produce natural food supplies for migratory waterfowl. San Luis also contains the most extensive network of pristine native grasslands, shrubs, and vernal pools that still remain within the Central Valley.

Thousands upon thousands of mallard, pintail, green-winged teal, and ring-necked ducks flock into the managed wetlands; while the colorful, yet secretive, wood duck lives throughout the tree-lined slough channels.

Herons and egrets nest in majestic oaks and willows, then feed on the refuge's abundant frog and crayfish populations. A wide diversity of songbirds, hawks, and owls also use refuge habitat.

Few areas in the Valley retain the flavor of early settlement days when wildlife was abundant, the air clear and fresh, and the landscape pleasant and pastoral. Encroaching agriculture and industry gradually reduced waterfowl habitat, and the vast marshes and great cattle herds gave way to intensive farming.

The San Luis National Wildlife Refuge encompasses over 26,600 acres of wetlands, riparian forests, native grasslands and vernal pools. A thriving population of the endemic tule elk is showcased by one of three auto tour routes. The refuge is host to significant assemblages of mammals, reptiles, amphibians, insects and plants; some of which, such as the blunt-nosed leopard lizard, tiger salamander, and San Joaquin kit fox, are endangered species.

From its earliest history, the San Joaquin Valley of Central California has been one of the principal wintering grounds for migratory waterfowl of the Pacific Flyway.

Early accounts by the first Spanish explorers abound in descriptions of the vast marsh areas of the Valley and its great flocks of ducks and geese in numbers darkening the sky. These marshes were formed by the overflow of water along rivers caused by fall and winter storms. Flooding continued into the summer, caused by runoff from melting snows in the high Sierra Nevada.

Much of the Valley was taken up by Spanish land grants and consisted of open range where cattle were raised. The discovery of gold in California attracted great hordes of people, and the meat from cattle became important as a source of food. During the 1850s and 1860s, cattle ranching was the major industry. During this period, great herds of tule elk, antelope, and deer were slaughtered to feed hungry miners; ducks and geese were killed by the wagonloads. In 1870, the Valley entered its present era of intensive agriculture.