The Santa Rosa Plateau is an upland plateau and southeastern extension of the Santa Ana Mountains in Riverside County, southern California. It is bounded by the rapidly urbanizing Inland Empire cities of Murrieta and Temecula to the northeast and southeast, respectively. The Santa Rosa Plateau Ecological Reserve preserves approximately 8,400 acres (34 km2) of the plateau, and includes the Moreno and Machado Adobes, Riverside County’s oldest standing structures, and other buildings from the 19th century Mexican land grant Rancho Santa Rosa.