Before about 11,000 years ago, herds of mammoths, camels, horses, pronghorns, and other large mammals inhabited what now is the Chihuahuan Desert. Deaths were numerous and provided food for the abundant scavengers. Among the birds dependent on carrion were the California Condor and the Caracara, both surviving, to the present. Extinct forms included the Western Vulture and the Brea Condor.
As species after species of large herbivores disappeared toward the end of the
Pleistocene Ice Age, the number of corpses decreased dramatically. The Brea Condor
became extinct, possibly out-competed by the California Condor. The Western Vulture
also vanished, or perhaps more likely, evolved into the smaller Black Vulture of today.
The Caracara mostly retreated southward. The California Condor, once ranging from New
York to the West Coast, retreated to the west, becoming limited to California and
Arizona in historic times. But a slight increase in the death rate during the last
century, probably due to humans, has now driven these magnificent birds to the very
brink of extinction in their California refuge. 
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.
Tarsometatarsi of four species of condors and vultures. The tarsometatarsus is the leg element just above the toes. From left to right: Modern specimen (UTEP Ornithology 68) of Cathartes aura, the Turkey Vulture (image reversed for comparison); fossil Coragyps occidentalis (UTEP Paleobiology 1.1029), Western Vulture; proximal two-thirds of tarsometatarsus (UTEP Paleobiology 32.122) of fossil Gymnogyps californianus, California Condor, image reversed; fossil (UTEP Paleobiology 1-1002) Breagyps clarki, La Brea Condor.
Howard, H. 1968. Limb measurements of the extinct vulture, Coragyps occidentalis. With a description of a new subspecies. Pp. 115-128, in Collected Papers in Honor of Lyndon Land Hargrave (A. H. Schroeder, ed.), Papers of the Archaeological Society of New Mexico, 1.
Howard, H. 1974. Postcranial elements of the extinct condor Breagyps clarki (Miller). Natural History Museum of Los Angeles County, Contributions in Science, 256:1-24.
Stock, C. [Revised by J. M. Harris]. 1992. Rancho La Brea. A record of Pleistocene life in California. 7th ed. Natural History Museum of Los Angeles County, Science Series 37:1-113.