Telegraph Peak is an 8,989-foot mountain in California’s San Gabriel Mountains, located within the San Gabriel Mountains National Monument and the Cucamonga Wilderness of the San Bernardino National Forest. It is the highest point in the Cucamonga Wilderness, giving it special geographic importance within this protected landscape. Geologically, its summit stands on cataclastic gneiss, while granodiorite underlies much of its southern side. Its significance rests chiefly in being the top high point of a preserved wilderness area in one of Southern California’s most familiar mountain ranges.