mount disappointment is a mountain in the san gabriel mountains in los angeles county, california with a summit elevation of 5,963+ feet (1,818+ m). it was named "disappointment" in 1894 when usgs surveyors sighted it from the santa susana mountains, believing it to be the highest point in the immediate area, decided to use it as their next triangulation point. when they reached the summit, however, they discovered that san gabriel peak half a mile (0.8 km) to the east was higher and it was a disappointment so they moved there instead.