Mount Disappointment in the L.A. San Gabriels has a summit elevation of 5,963+ feet . It was named when 1894 USGS surveyors reached the summit and discovered that San Gabriel Peak half a mile to the east was 167 feet higher.
A Nike missile site was located there in 1956 and the summit was flattened to accommodate it. The missile site was deactivated in "61, and abandoned in "65. You can now hike the 4.4 mi. summit trail.