Imperial National Wildlife Refuge

This large Refuge straddles the lower Colorado River for 58 kilometers (36 miles). Most of the area is on the Arizona side. On the California side it is split by the Picacho State Recreation Area. At the southern end of the Refuge is the Imperial Dam, which creates a large, shallow reservoir; this, and the low gradient of the river in its lower reaches, have formed numerous sloughs, backwater lakes, embayments, and a number of marshes. On both sides of the river are desert mountains, the Chocolates on the California side.

Along the river there is a mixed riparian community with cattail, Typha sp., bulrush, Scirpus americanus, arrowweed, Pluchea sericea, tamarisk, Tamarix aphylla, cottonwood, Populus fremontii, Goodding willow, Salix gooddingii, and Western hackberry, Celtis reticulata. In the mountainous area above the river and in the washes, desert scrub predominates, with mesquite, Prosopis glandulosa var. torreyana, desert ironwood, Olneya tesota, various Opuntias including beavertail, Opuntia basilaris, and ocotillo, Fouquieria splendens.

Over 266 species of birds have been recorded from the Refuge, including the endangered Yuma clapper rail, Rallus longirostris yumanensis, and the peregrine falcon, Falco peregrinus.

A number of ducks and geese and various shorebirds will be found on the Refuge during the migratory season, some of whom winter here. Among the more uncommon birds seen here are the wood ibis, Mycteria americana, prairie falcon, Falco mexicanus, and the reddish egret, Dichromanassa rufescens, the latter of irregular occurrence.

Among the mammals, 39 species have been sighted, including the desert bighorn, Ovis canadensis, bobcat, Lynx rufus, beaver, Castor canadensis, and numerous rodents such as the longtail and spiny pocket mouse, Perognathus formosus and Perognathus spinatus, and the whitetail antelope squirrel, Citellus leucurus, whose range limit is the Colorado River. Feral burro and pigs are present in the area as well.

Numerous reptiles are found in the Refuge, including the protected desert tortoise, Gopherus agassizi.

The Chocolate Mountains are rugged Tertiary volcanics, rhyolites, andesites and pyroclastics, with some Miocene fanglomerates and, in the washes and valley proper, Quaternary alluvium.

Integrity: The damming of the river has altered the habitat considerably. Though there is little development in the Refuge proper, the are pockets of development along the river, including the recreation area.

Use: Educational, research, observational, hunting, fishing.

March 1976