Black Mountain is an extended ridge crest in the Diablo Range of southwestern Fresno County, California, south of Reef Ridge and north-northeast of Parkfield. Its eastern end begins west of Zwang Peak, and the ridge runs west at elevations above 4,000 feet, rising to 4,345 feet near its middle before reaching Castle Mountain at 4,343 feet. From there it turns west-northwest for about 2 more miles, remaining above 3,790 feet and carrying several peaks above 3,800 feet before joining another east-west ridge from Mustang Peak. West of Castle Mountain, the crest forms the Fresno-Monterey county line, marks the San Joaquin Valley watershed, and includes the source of Canoas Creek on its far eastern north slope.