With scarcely a break, the Park Range-Gore Range structure continues
southward into the Tenmile and Mosquito Ranges. These high ridges
separate South Park from the upper Arkansas Valley, and include a
cluster of very high peaks, Quandary, Mt. Lincoln, Mt. Democrat, and Mt.
Bross, all over 14,000 feet in elevation.
Structurally, both the Tenmile Range and the Mosquito Range are highly
asymmetrical anticlines, gentle on the east and steeply faulted on the
west. Paleozoic sedimentary rock layers containing many fossils cover
large portions of the higher parts of these ranges, but two of the
highest peaks, Mt. Bross and Mt. Lincoln, are capped by the Lincoln
Porphyry, a Tertiary intrusive, while Quandary Peak is Precambrian
granite.
These mountains are highly mineralized, and have been extensively
explored and mined. The Climax Molybdenum Corporation operates an
especially large mine at Climax, and the New Jersey Zinc Company has a
large underground mine and mill at Gilman, on the western slopes of
Tenmile Range.
Buffalo Peaks, two highly eroded volcanic mountains near the south end
of Mosquito Range, are extrusions of lava and ash which have buried the
axis of the Mosquito uplift. They are major volcanoes related to a group
of small volcanic cones near Antero Junction, in South Park.
South of Buffalo Peaks, near Trout Creek Pass, the Mosquito Range loses
altitude rapidly and merges with the rough country called the Arkansas
Hills. Cinder cones, dikes, and other evidences of Tertiary volcanic
activity can be seen between Trout Creek Pass and Salida.