Rabbit Peak is a 6,653-foot mountain in the southern Santa Rosa Mountains of California’s Peninsular Ranges, in Riverside County near the San Diego County line and Anza-Borrego Desert State Park. About 14 miles northeast of Borrego Springs and 20 miles south of Indio, it is notable less for great height than for the exceptional difficulty of reaching its summit. Even its easiest ascent requires more than 6,000 feet of elevation gain over rugged, trailless, waterless desert terrain. For that reason, it has been regarded as the hardest mountain to climb in Southern California, demanding unusual endurance rather than technical climbing skill.