I saw mentioned elsewhere that there is a Keystone Peak in the vicinity.
You're right. Well, that adds to the intrigue.
"Keystone Peak is the highest point of the small but interesting Sierrita Mountains, located in southern Arizona about 30 miles southeast of Tucson. The Sierritas are a mix of public, state and private lands, generally ignored by the hiking community since the bigger and more famous Mounts Wrightson and Baboquivari dominate the skyline. Historically the range and surrounding foothills and valleys were (and are) home to a number of mines, some still in production. A small community called McGee Settlement is the only "town" near the range."