Anza Valley, formerly known as the Hamilton Plains,[1] is a basin in Riverside County, California. Anza Valley trends southwest from Bautista Canyon, west of Thomas Mountain to Terwilliger Valley, 2.8 miles west-southwest of Table Mountain and 12 miles south of Idyllwild. The valley lies at an elevation of 4,157 feet (1,267 m), west of the San Jacinto and Santa Rosa Mountains. It is drained by Cahuilla Creek, a tributary of the Santa Margarita River.[2]