Paul Remeika and Lowell Lindsay in the book "Geology of Anza-Borrego: Edge of Creation," give us a geologist's perspective of this area.

Millions of years ago, say the authors, these badlands looked vastly different than they do today. Ground sloth and mountain deer roamed here. Herds of grazing equids (horses, zebras, and asses) and camelids (large species of camel and stilt-legged llamas) were also plentiful, according to the rich fossil deposits found in the area. Each was spied upon by predatory cats, such as the saber-tooth Smilodon gracilis and Smilodon fatalis (California's state fossil) as well as the American lion, Panthera atrox. There were abundant canids (dire wolves and coyotes), too. Airborne, above open grasslands and sagebrush, daily flybys of hawk, eagle and giant vultures such as Terratornis incredibilis, worked over carrion and microtine rodents.