<<Prev Home PDF Next>>
The Origin of Comb Ridge
Robert Fillmore, Western State College of Colorado in Gunnison, CO
(An excerpt and images from his new book: Geological Evolution of the Colorado Plateau)
Comb
Ridge is a lofty sinuous spine of red sandstone that stretches over 80
miles across northern Arizona and southeast Utah. This monocline, as
these structures are called, begins near Kayenta and snakes northward
to fade away near the west flank of the Abajo Mountains. Monoclines are
a peculiar component of the Colorado Plateau, with their long ridges of
steeply tilted strata in a region otherwise known for its miles of
flat-lying sedimentary rocks. They are hard to miss. Although not
confined to the Colorado Plateau, their concentration here is unique.
Similar structures make up the San Rafael Swell, Capitol reef, and
Colorado National monument near Grand Junction. All are closely related
in origin and timing.
ramp
of Comb Ridge. Another notable result of this uplift is the ensuing
deep incision into the uplift by energized rivers as their runoff seeks
a path to lower elevations. The deep narrow canyons of Cedar Mesa owe
their existence to Monument Upwarp.
Monoclines are a peculiar component
of the Colorado Plateau, with their long ridges
of steeply tilted strata in a region
otherwise known for its miles of
flat-lying sedimentary rocks.
They are hard to miss.
The
term monocline refers to a single-limbed fold; in simple geometric
terms, a gargantuan ramp. The ramp of steeply tilted strata separates
uplifted regions from those that have dropped downwards, relatively
speaking. At Comb Ridge the uplifted region lies to the west in the
form of Monument Upwarp, which includes Cedar Mesa, the San Juan River
Canyon, and Monument Valley. The net result is older Paleozoic rocks to
the west separated from younger Mesozoic rocks immediately east by the
colossal
The
monoclines formed at the same time as the jagged Rocky Mountains of
Colorado and Wyoming. This mountain-building svent is the result of a
widespread pulse of compression that rippled across western North
America 65 to 50 million years ago. The stronger crust of the Colorado
Plateau resisted the large scale uplift of alpine mountains but did not
escape unscathed.
next page
Geological Evolution of the Colorado Plateau By Robert Fillmore
Robert
Fillmore's clear, easy-to-read text documents spectacular features of
the eastern Colorado Plateau, one of the most interesting and scenic
geologic regions in the world. The area covered in detail stretches
from the Book Cliffs to the deep canyons of the San Juan River area.
The events that shaped this vast region are clearly described and
include the most recent interpretations of ongoing geologic forces. The
book also includes mile-by-mile road logs with explanations of the
various features for most of the scenic roads in the region, including
Arches National Park, Canyonlands National Park, and the Natural
Bridges area.
Robert
Fillmore is professor of geology at Western State College of Colorado
in Gunnison. He is the author of Geology of the Parks, Monuments, and
Wildlands of Southern Utah.
<<Prev Home PDF Next>>