The 665,400 acres Kofa NWR was established in the Lower Sonoran Desert ecosystem primarily to preserve desert bighorn sheep and unique Sonoran Desert vegetation.

Vegetation is relatively sparse throughout, with the exception of tree and shrub corridors along dry washes that descend to alluvial fans and basins from the desert mountains. Creosote, ironwood, palo verde, ocotillo and mesquite comprise much of the vegetation with many types of cacti, most notably the saguaro and cholla species.

Major wildlife species include desert bighorn sheep, mule deer, kit fox, 188 species of birds (87 Neotropical), desert tortoise, several species of bats, 5 species of rattlesnakes, and numerous other reptiles.

The refuge contains 516,300 acres of official wilderness spread over 3 major mountain ranges (Kofa, Castle Dome, and New Water Mountains). Elevations range from 680 feet on the desert floor to 4,877 feet atop Signal peak.

Temperatures range from lows near 25 degrees F. in the months of December and January to highs that may exceed 115 degrees F. from July through September. Precipitation generally ranges from 2 to 8 inches per year.