Six subspecies of mule deer inhabit roughly 88,000 square miles or just over half of California's lands. The Columbian black-tailed deer, the Rocky Mountain mule deer and the California mule deer reside in scattered habitats across the state's northern counties. All six subspecies look very similar with only slight differences in coat color and markings.
Columbian Black-Tailed Deer
Columbian black-tailed deer are the most abundant subspecies in California. They occur in much of northern California, in coastal areas from the Oregon border to Santa Barbara county and inland to the western slope of the Cascade-Sierra Nevada Range. Some of these populations are migratory, spending summers in the mountains and winters at lower elevations. Others, especially those near the coasts, are year-round residents. True to their name, Columbian black-tailed deer have entirely black tails and a relatively small rump patch
Rocky Mountain Mule Deer
Rocky Mountain mule deer, the third most abundant subspecies in the state, occur in primarily east of the Cascade-Sierra Nevada Range in Lassen, Shasta, Siskiyou and Modoc counties. They generally spend winters in the Great Basin Desert feeding on bitterbrush and sagebrush. In the summers, they travel upwards of 50 air miles to high-elevation ranges in the mountains. Rocky Mountain mule deer are among the largest of the subspecies and as a rule, have the largest antlers. They have a large, white rump patch, and a tail that is only black at the tip.
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California Mule Deer
The second most abundant subspecies in the state, the California mule deer, ranges along the west slope of the Sierra Nevada, as well as in the San Bernardino, San Gabriel and Tehachapi mountains. Both resident and migratory populations occur. California mule deer have a larger rump patch and less black on their tail than the Columbian black-tailed deer. The tail may appear to have a black line running its length. They're often confused with southern mule deer, which has a considerably larger strip of black.
Because they are the same species, California's mule deer subspecies can and do readily interbreed when they come into contact with one another. In Coastal areas south of the San Francisco Bay area, California mule deer hybridize extensively with Columbian black-tailed deer.