Otay Mountain Wilderness is a protected wild landscape in southern San Diego County, encompassing 18,500 acres of steep hills and canyon country in the San Ysidro Mountains near the Mexico–United States border. Designated wilderness in 1998 and preserved within the National Wilderness Preservation System, it is valued as one of western San Diego County’s last pristine public lands and as a key part of regional species conservation. Its ancient volcanic soils support rare chaparral and sagebrush habitats, including the world’s largest stand of Tecate cypress and many sensitive plants. Its border location has also brought wall and road construction whose environmental effects have directly challenged this protected landscape.