Diamond Valley Lake is located within the Domenigoni/Diamond valleys, between the Domenigoni Mountains and Rawson Mountains, southwest of the city of Hemet. The site was chosen because of its location between the cities of San Diego and Los Angeles, and because of the raw materials located on-site for the construction of the three dams. The location was also chosen because of its proximity, about , to the existing Colorado River Aqueduct that supplies the lake with water.