Mount Lemmon, Mountain peak in Coronado National Forest, Arizona.

Mount Lemmon rises to 9,171 feet (2,795 m) as the highest summit of the Santa Catalina Mountains in Coronado National Forest north of Tucson. Its upper slopes are built of Bolsa Quartzite, Dripping Spring Quartzite and local sandstone and conglomerate, cut by a Diabase Dike of the Apache Group. Bare pale grey and tan rock, ridged and gullied, drops steeply into a deep valley, with sparse trees and shrubs on the ledges and boulders on the granite-like foreground ledge.

Sara Plummer Lemmon reached the summit in 1881 with her husband and rancher E. O. Stratton, on horse and on foot, and the mountain was later named for her. The Tohono O'odham know it as Babad Do'ag, Frog Mountain. Before the Catalina Highway was built, the only route to the top was an unpaved road from Oracle on the north side.

The SkyCenter takes advantage of dark skies and dry air for nighttime observation, offering programs that bring astronomy closer to visitors who come for the view. Clear conditions at this elevation attract both researchers and amateur stargazers working far from city lights.

The Catalina Highway winds upward on switchbacks and provides access to hiking trails, picnic areas, and camping spots along the way. Drivers in summer should bring warmer clothing, as temperature drops noticeably with elevation.

The drive upward passes through six distinct ecological zones, equivalent to a cross-section from Mexico to Canada, experienced within a few dozen kilometers. At the upper end sits the southernmost ski resort in the continental United States, allowing for snow activities during winter months.