Otay Mountain Wilderness, Protected wilderness area in San Diego County, US.

Otay Mountain Wilderness is a protected mountainous area covering more than 16,000 acres (6,500 hectares) located along the California-Mexico border. The terrain rises to nearly 3,500 feet (1,100 meters) and features a rugged landscape with canyons, ridges, and native plants adapted to arid conditions.

Wilderness status was conferred on October 7, 1998, placing 18,500 acres under the Wilderness Act within the National Wilderness Preservation System. President Bill Clinton signed the legislation on December 11, 1999. The Bureau of Land Management manages the area. In December 2008, construction of the border wall continued through the wilderness under the Secure Fence Act of 2006.

The name Otay comes from the Kumeyaay village of Otai, and the mountain's slopes were used for hunting and gathering before becoming a protected wilderness. Today, the area is valued for its role in San Diego's multi-species conservation plan, which coordinates habitat protection across public and private lands.

The wilderness lies 12 miles east of Otay Mesa, just north of the Mexico–United States border, and is managed by the Bureau of Land Management. Terrain is extremely rugged, with steep canyon walls and hills, and the summit of Otay Mountain reaches 3,566 feet. Bring maps and water; there are no facilities or marked trails.

The world's largest stand of Tecate cypress grows here, and at least five plant species, including that cypress, occur only on Otay Mountain or in the immediate area. In all, 37 plants on the mountain are listed as sensitive by the California Native Plant Society.