Casa de Oro-Mount Helix is a census-designated place (CDP) in San Diego County, California. The CDP encompasses several neighborhoods in unincorporated parts of the county near the cities of El Cajon and La Mesa as well as part of the unincorporated community of Spring Valley. The CDP gets its name from the neighborhood of Casa de Oro, which straddles the line between Spring Valley and unincorporated El Cajon, and Mount Helix, a prominent hill in La Mesa.