Mount Thayer is a 3,502-foot peak in California’s Santa Cruz Mountains in Santa Clara County, with its summit about 1.5 miles northwest of Mount Umunhum. The mountain lies within part of the abandoned Almaden Air Force Station, linking it to the area’s former military use. At its summit stands an old derelict building ringed by telephone poles, physical remnants of that past. Because the mountain and its surrounding property are off limits to the public, these features remain part of a closed landscape shaped by both natural geography and military history.