Most of the individual ranges making up the Rocky Mountains in Colorado
are the result of highly localized movements of the crust as the entire
region was thrust upward from below. These movements broke the deep,
massive igneous and metamorphic rocks of the Precambrian basement, and
bent the more flexible Paleozoic and Mesozoic layered rocks above them
until they arched upward in a series of corrugations. The mountains thus
formed are known to geologists as _faulted anticlines_.
As the mountains rose, they were of course attacked by the forces of
erosion. The sedimentary layers were completely stripped from the crests
of many of the uplifts, so that Precambrian rocks were exposed. It is
these rocks which form the summits of the highest peaks of Colorado. As
with all rules, there are exceptions: the Spanish Peaks are volcanic,
and the crest of the Sangre de Cristo Range is composed of sedimentary
rocks.
The trend of most of the ranges in Colorado is north-south, swinging to
northwest-southeast near the southern end. Surprisingly, in the
northwestern corner of the state there is an east-west trending range,
the Uinta Mountains.
Fifty or more mountain ridges in Colorado have been named as separate
ranges. Of these, the most prominent, frequently visited ones will be
discussed here.