Anza-Borrego Desert State Park in southern California is the largest state park in the state and the second largest in the United States . The park is located on the eastern side of San Diego County, with portions extending east into Imperial County and north into Riverside County. It is about a two-hour drive from San Diego, Riverside and Palm Springs. The park is named after Spanish explorer Juan Bautista de Anza and the Spanish word borrego, or bighorn sheep.