The San Benito Mountain region of the southern Diablo Range, San Benito and Fresno counties, California, is of unusual biological interest for several reasons. The highest peaks, San Benito Mountain (5241 ft [1599 m]) and Santa Rita Peak (5165 ft [1575 m]), support on their upper slopes significant forest well isolated from such growth in other areas. The nearest major stands of mixed conifers appear approximately 50 miles (80 km) to the west, in the northern Santa Lucia Range, Monterey County. Eastward, a distance of approximately 93 miles (150 km) separates the San Benito conifers from the rich forests of the Sierra Nevada (Figure 1).