Echo Mountain, Mountain summit in San Gabriel Mountains, California.

Echo Mountain is a summit in the San Gabriel Mountains above Altadena, in Southern California, reachable by steep trails running through Rubio and Las Flores canyons inside Angeles National Forest. The peak sits on an open rocky platform surrounded by chaparral scrub, with views across the valley that stretch toward distant ridges on clear days.

Echo Mountain, also called Mount Echo, was listed on January 6, 1993, as part of the Mount Lowe Railway monument area on the National Register of Historic Places. At the summit are the ruins of White City, a resort served by the Mount Lowe Railway, whose Great Incline funicular ran from the point down to Rubio Canyon. Its white cars could be seen ascending and descending the slope.

The name comes from the repetitions a voice could make in Castle Canyon below. Boy Scout projects searched for the "sweet spot" with the most repetitions, and during the Mount Lowe Railway era echophones were set up near the best spots to help project voices.

The main trail begins at the end of Lake Avenue in Altadena and climbs through switchbacks with steep sections, so solid footwear and a reasonable level of fitness are needed. Starting early in the day is a good idea, particularly in summer, to avoid the worst heat and allow enough daylight for the return.

The name Echo Mountain comes from the repetitions of a voice in Castle Canyon. Boy Scouts searched for the "sweet spot" with the most echoes, and during the Mount Lowe Railway era echophones were placed near the best spots to help project voices.