Description & Facts: El Cajon is a city in San Diego County in Southern California. The local San Diego Trolley light rail system serves El Cajon with two lines: the Orange Line, which travels through La Mesa and Lemon Grove to Downtown San Diego, and the Green Line which heads past SDSU and through Mission Valley to San Diego's Old Town. El Cajon has two stations, which are served by both lines: the El Cajon Transit Center at Palm and Marshall Avenues, and the Arnele Avenue station at Arnele and Marshall Avenues.