Black Mountain is a lava-capped mesa on the San Xavier Indian Reservation in Pima County, Arizona, southwest of Tucson. Rising about 1,000 feet above its base to 3,700 feet, it stands out as a distinct ridge along Mission Road. Its importance extends beyond geology to the archaeological remains on its summit, where an ancient Hohokam fortification includes long stone walls, circular stone rings, petroglyphs, man-made trails, and pottery sherds. About 3.18 miles southwest of Mission San Xavier del Bac, the site connects the Tucson basin landscape to a much longer human history. Because it lies on reservation land, the summit ruins are not open to the general public.