Echo Mountain is a mountain promontory of the San Gabriel Mountains, in the Angeles National Forest above Altadena, in Los Angeles County, California. Echo Mountain was shaped from an alluvial fan between Rubio and Las Flores canyons. It is geographically defined by Castle Canyon to its leeward side, Rubio Canyon at its foot, and Las Flores Canyon on …Echo Mountain is a mountain promontory of the San Gabriel Mountains, in the Angeles National Forest above Altadena, in Los Angeles County, California. Echo Mountain was shaped from an alluvial fan between Rubio and Las Flores canyons. It is geographically defined by Castle Canyon to its leeward side, Rubio Canyon at its foot, and Las Flores Canyon on its windward side. Echo has a mean elevation of 3,207 feet. It is most visible as a short mountain extension whose ridge protrudes below the peak of Inspiration Point.