Mount Disappointment, Mountain summit in San Gabriel Mountains, California, US.

Mount Disappointment is a summit in the San Gabriel Mountains of Los Angeles County, California, reaching 5,963+ feet (1,818+ m). Its top was flattened in 1955 for a Nike missile site and now holds telecommunications equipment for commercial and government organizations. San Gabriel Peak, half a mile (0.8 km) to the east, rises 167 feet (51 m) higher.

In 1894 USGS surveyors of the Wheeler Survey sighted the peak from the Santa Susana Mountains and took it for the highest point nearby, choosing it as their next triangulation station. On the summit they found San Gabriel Peak, half a mile east, stood 167 feet higher, so they moved there and the mountain kept the name Disappointment. A Nike missile site was built on the summit in 1955, flattening it, and was abandoned in 1965.

The name Disappointment dates from 1894, when USGS surveyors reached the summit and found San Gabriel Peak, half a mile east, stood 167 feet higher. The flattened top left by the Nike missile site, abandoned in 1965, now holds commercial and government telecommunications equipment.

Visitors should bring sturdy footwear and plenty of water since the trails feature numerous elevation changes and exposed sections. Early morning is the best time to hike when temperatures are cooler and visibility is clearer.

The summit was flattened in 1955 to hold a Nike missile site, which was abandoned in 1965; the leveled top now carries commercial and government telecommunications equipment. San Gabriel Peak, 0.8 km east, is 51 m higher.