Bordering the Arkansas River valley on the west, the Sawatch Range
includes Colorado’s highest mountain, Mt. Elbert (14,417 feet). With
several other 14,000-foot summits, this range is the highest in the
state. One group of peaks, known as the Collegiate Range (Mts. Harvard,
Yale, Columbia, and Princeton) forms a particularly imposing vista from
U. S. highway 24 between Trout Creek Pass and Buena Vista. The
Independence Pass highway (Colorado 82) between Leadville and Aspen
penetrates the heart of the Sawatch high country.
The Sawatch Range as a whole is about 100 miles long (north to south)
and 40 miles wide. It is a great faulted anticline intruded by igneous
rocks. The high area north of Leadville shows that the Sawatch and
Mosquito Ranges are in reality one huge dome with a slight sag in the
middle. The ranges, though, are sharply separated topographically by the
deep valley of the Arkansas River. Precambrian rocks are near the
surface between the ranges, hidden only by a thin cover of stream
gravels. Near Leadville, some complexly faulted Paleozoic limestones lie
in the sag between the ranges.
At Mt. Princeton Hot Springs there is evidence of repeated faulting and
igneous activity. The rocks are strongly altered by hot water coming to
the surface through fissures and cracks.
On the west side of the Sawatch range, the old mining towns of Tincup
and Aspen grew up where limestone and sandstone layers, broken and
crumpled as the Sawatch Range rose, were mineralized by solutions rich
in gold and silver. The Aspen Mining District was studied extensively by
geologists of the U.S. Geological Survey, and their maps show almost
unbelievable complexity in the faulting of the rock layers which exist
there.
The north end of the Sawatch Range plunges under shales and sandstones
along the Eagle River east of Wolcott. Gypsum in the sediments here has
acted like putty: the layers of rock in which it was deposited have
become peculiarly crumpled, making the area along the Eagle River
(visible from U. S. Interstate 70) between Avon and Edwards hummocky and
irregular. Vegetation is unusually sparse here because of gypsum in the
soil.
About midway between Edwards and Wolcott, the Eagle River suddenly
changes direction and flows northward for about a mile before resuming
its former westward course. This sudden change is caused by a sharp
north-south fold in the sedimentary rocks on the northwestern flank of
the Sawatch Range. A magnificent series of roadcut and hillside
exposures along the highway here illustrates the close relation between
rock layers and river course. Within about a mile, the highway cuts
through rocks of Pennsylanian, Permian, Triassic, Jurassic, and
Cretaceous age, spanning a geologic time interval of more than 200
million years.
The south end of the Sawatch Range, at Monarch Pass, contains steeply
dipping Late Paleozoic limestones and coal beds. The coal has been mined
on a small scale; the limestone is now quarried for use as a flux in
iron smelters at Pueblo.
[Illustration: The area below the Aspen Mountain ski lift is highly
complex geologically. It is particularly well known because of
extensive prospecting and mining activity in the region.]