 Although European foxes were introduced to portions of the United States in the 1900s recent genetic investigation indicates an absence of European fox haplotypes in any North American populations.Also, introduced eastern red foxes have colonized southern California, the San Joaquin Valley, and San Francisco Bay Area, but appear to have mixed with the Sacramento Valley red fox ("V. fulva patwin") only in a narrow hybrid zone.In addition, no evidence is seen of interbreeding of eastern red foxes in California with the montane Sierra Nevada red fox "V. v. necator" or other populations in the Intermountain West (between the Rocky Mountains to the east and the Cascade and Sierra Nevada ranges to the west.