San Gorgonio Mountain, also known as Mount San Gorgonio or Old Greyback, is Southern California’s highest peak and the loftiest summit in the Transverse Ranges. Rising in the San Bernardino Mountains, it is especially notable for its great topographic prominence, its broad plateau-like form, and its snow-capped visibility across the region, including from Mount Whitney 190 miles away. The mountain marks an important watershed divide, with the Santa Ana, Whitewater, and San Gorgonio rivers beginning there. Composed mainly of quartz monzonite over older Precambrian rocks, it is accessible by strenuous but technically easy hiking routes and is also remembered for fatal aircraft crashes in 1952 and 1977.