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Home/Lake Powell and Glen Canyon Geology/Monoclines

Monoclines

Aerial View of Glen Canyon showing angles of rock layers | Photo by Gary Ladd
Aerial View of Glen Canyon showing angles of rock layers | Photo by Gary Ladd

The Colorado Plateau is characterized by a thick sequence of mostly sedimentary rock layers that have been uplifted thousands of feet by plate tectonics movements. The uplift began about 70 million years ago, thus ending almost all sedimentary rock layer creation.

Normally such tectonic activity warps and buckles the original flat-lying sedimentary rock layers until they are severely tilted and twisted. In every direction around the Colorado Plateau (the Rocky Mountains to the east and north, the Basin and Range Province to the west and south) sedimentary rock layers are exactly this way—tilted and twisted. But this is never true within the Colorado Plateau. Well, almost never.

Because tilts and twists of the rock layers are relatively uncommon in the Colorado Plateau, wherever they do occur they stand out theatrically. For instance, there’s the dramatic Waterpocket Fold featured in Capitol Reef National Park and there’s Comb Ridge that crosses the San Juan River west of Mexican Hat, Utah.

Based upon their orientation and shape, folds in the rock are categorized by geologists as synclines, anticlines or monoclines. Folds that bend down then back up (like a trough) are called synclines, folds that arch upwards and back down again (like a hill) are called anticlines.

And then there are monoclines, folds that are simply half of one of the other types, high on one side and low on the other (like a ramp). All three of these shapes are evidence of times when the crust of the Colorado Plateau was subjected to compressive forces from the jostling of tectonic plates.

In the case of the most prominent Colorado Plateau rock folds, the compressional events occurred about 65 million years ago at about the same time that the most recent version of the Rocky Mountains was being created to the east.

It turns out that monoclines play a critical role in creating the setting that eventually led to the formation of both Grand Canyon and Glen Canyon.

Throughout the length of Glen Canyon its rock layers remain mostly flat-lying. To someone riding in a boat along the flat surface of Lake Powell, the shoreline rock layers in most areas undulate gently throughout the length of Glen Canyon. So far, so good.

But just before the Colorado River (downstream of Glen Canyon Dam) exits Glen Canyon the enclosing rock layers tilt up about 2,500 feet rapidly and conspicuously. In these final few miles of Glen Canyon, the Colorado River crosses the Echo Cliffs Monocline, running roughly north and south.

The uplift brings older rock units to the surface and the first of these is our old friend the Kaibab Formation, Grand Canyon’s rimrock layer. The emergence of the Kaibab from river level marks the beginning of the Grand Canyon. Glen Canyon has ended.

It is difficult to overemphasize the importance of the Lees Ferry area. It marks the end of Glen Canyon, the beginning of Grand Canyon, the stratigraphic location of the Great Dying extinction event in the local rock sequence, and therefore the transition from Paleozoic to Mesozoic time.

If that is not enough, Lees Ferry is the place where humans long ago found a surprisingly accessible and easy crossing of the Colorado River. (It is relatively easy to cross the Colorado River here because the lowest-most rock units of the Mesozoic, the Moenkopi, and the Chine Formations are mostly soft and easily eroded. Therefore no cliffs of resistant rock guard way to the edge of the river at Lees Ferry.)

About 70 miles downstream from Lees Ferry the Colorado River encounters a second massive monocline. This one also runs north and south. The Colorado River seems to enjoy the challenge of hitting older, rock units because it turns directly into the face of the East Kaibab Monocline and drills in.

The result is a Grand Canyon that suddenly jumps from about 3,000 feet deep to 5,000 feet deep as the older and highly resistant rock sequence rises higher and higher to the west.

In summary, it is not only the rock layers themselves that determine the look and structure of the canyons; it’s the later folding and faulting of those rock layers, too.

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Gary Ladd’s Publications

Photographing Grand Canyon: Where, When, and How to Capture the Best Photos
Photographing Grand Canyon: Where, When, and How to Capture the Best Photos
  • Gary Ladd (Author)
  • English (Publication Language)
  • 64 Pages - 03/30/2016 (Publication Date) - Grand Canyon Conservancy (Publisher)
$18.75
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Grand Canyon: Views beyond the Beauty
Grand Canyon: Views beyond the Beauty
  • Used Book in Good Condition
  • Ladd, Gary (Author)
  • English (Publication Language)
  • 82 Pages - 09/01/2008 (Publication Date) - Grand Canyon Association (Publisher)
$1.59
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Lake Powell: A Photographic Essay of Glen Canyon National Recreation Area (Companion Press...
Lake Powell: A Photographic Essay of Glen Canyon National Recreation Area (Companion Press...
  • Used Book in Good Condition
  • Markward, Anne (Author)
  • English (Publication Language)
  • 96 Pages - 08/01/2009 (Publication Date) - Mountain Press Publishing Company (Publisher)
$1.59
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Glen Canyon: Images of a Lost World
Glen Canyon: Images of a Lost World
  • Used Book in Good Condition
  • Nichols, Tad (Author)
  • English (Publication Language)
  • 176 Pages - 02/06/2023 (Publication Date) - Museum of New Mexico Press (Publisher)
$520.57
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Gary Ladd's Canyon Light: Grand Canyon & Lake Powell (Cerca Book)
Gary Ladd's Canyon Light: Grand Canyon & Lake Powell (Cerca Book)
  • Used Book in Good Condition
  • Hardcover Book
  • Ladd, Gary (Author)
  • English (Publication Language)
  • 160 Pages - 01/01/2010 (Publication Date) - Stephens Press LLC (Publisher)
$7.03
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Grand Canyon: Time Below the Rim
Grand Canyon: Time Below the Rim
  • Used Book in Good Condition
  • Hardcover Book
  • Childs, Craig Leland (Author)
  • English (Publication Language)
  • 192 Pages - 02/05/1999 (Publication Date) - Arizona Highways (Publisher)
$19.28
Buy on Amazon Price incl. tax, excl. shipping

Last update on 2023-02-05 / Affiliate links / Images from Amazon Product Advertising API

Published on: October 10, 2012

Categories: Lake Powell and Glen Canyon GeologyTags: Colorado Plateau, Echo Cliffs Monocline, Glen Canyon, Grand Canyon, Kaibab Formation, Lees Ferry, Mesozoic, monoclines, Paleozoic, sedimentary rock layers, tectonics movement, uplift, Waterpocket Fold

About Gary Ladd

Gary Ladd is a renowned Southwest photographer and author of numerous books including “Page, Arizona: Hub of the Visual Universe”, "Glen Canyon: Images of a Lost World", "Grand Canyon: Time Below the Rim", and "Lake Powell: A Photographic Essay of Glen Canyon National Recreation Area."

A resident of Arizona for over thirty years, Gary has spent the last twenty-five years seriously hiking, exploring, and photographing the astonishing beauty of the Colorado Plateau, particularly Glen and Grand Canyons.

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