The mountains are faulted anticlines formed as part of the Sawatch Uplift during the Laramide orogeny approximately 65 MYA.
The mountains were originally contiguous with the higher Sawatch Range to the west but were separated during the formation of the rift valley at the headwaters of the Arkansas River approximately 35 MYA.
 The range is primarily of granite.
The eastern flank of the range along the rim of South Park overlain by Paleozoic and Mesozoic sedimentary rocks.
The northern end of the range was glaciated during Pleistocene time, forming u-shaped valleys in the canyons.

The high ridge of the range forms a relatively difficult barrier between South Park and the Arkansas headwaters.
Several of the high peaks of the range are prominently visible from the southern side of Fremont Pass along State Highway 91 between Climax and Leadville.
The range is not traversed by any major highway, but only in two places  by backroads over high passes: Mosquito Pass and Weston Pass.
Much of the range is located within the Pike National Forest.
The mountains are faulted anticlines formed as part of the Sawatch Uplift during the Laramide orogeny approximately 65 MYA. The mountains were originally contiguous with the higher Sawatch Range to the west but were separated during the formation of the rift valley at the headwaters of the Arkansas River approximately 35 MYA.  The range is primarily of granite. The eastern flank of the range along the rim of South Park overlain by Paleozoic and Mesozoic sedimentary rocks. The northern end of the range was glaciated during Pleistocene time, forming u-shaped valleys in the canyons.
The high ridge of the range forms a relatively difficult barrier between South Park and the Arkansas headwaters. Several of the high peaks of the range are prominently visible from the southern side of Fremont Pass along State Highway 91 between Climax and Leadville. The range is not traversed by any major highway, but only in two places  by backroads over high passes: Mosquito Pass and Weston Pass. Much of the range is located within the Pike National Forest.
Mosquito Range