GEOLOGY OF NATIONAL PARKS
Glen Canyon National Recreation Area
Note: Slide numbers refer to the PowerPoint presentation which accompanies the lecture.
Glen Canyon, slide 1 here
Glen Canyon, slides 2 here
Glen Canyon NRA “stretches for hundreds of miles from Lees Ferry in Arizona to the Orange Cliffs of southern Utah, encompassing scenic vistas, geologic wonders, and a panorama of human history. Additionally, the controversy surrounding the construction of Glen Canyon Dam and the creation of Lake Powell contributed to the birth of the modern day environmental movement”. (NPS Glen Canyon Web Site)
Glen Canyon, slide 3 here
John Wesley Powell was the first person to fully explore and write about the canyons of the Colorado River. On the first of two trips down the Colorado, Powell and his men saw and named many features, including Glen Canyon. Though several people, both before and after Powell, lived, worked, and traveled in Glen Canyon, it remained a place largely unknown to most of the United States. It was still terra incognita in the early 1950's when the Bureau of Reclamation proposed building a dam, one of many proposed for the Colorado River, at Glen Canyon's southern end.
The nation's environmental movement, though still in its infancy at this time, had just waged a successful campaign (led by the Sierra Club) to prevent the construction of a dam at Echo Park in Dinosaur National Monument. The wonders of Glen Canyon, however, were still undiscovered by those who might have preserved it. “Now I admit that nature can't improve upon man. We're probably the supreme being." (Quote from Floyd Dominy, commisioner of the U.S. Bureau of Reclamation from 1959 to 1969.) Attitudes like those expressed by Dominy have lead to a much stronger environmental movement today than at the time Glen Canyon dam was under consideration. They also led Katie Lee, folk singer, river runner, frequent visitor to the canyon, and environmental activist, to rename the Bureau of Reclamation as the “Wreck the Nation” bureau.
Glen Canyon, slide 4 here
Today, Glen Canyon Dam has created Lake Powell, ironically named for the one-armed civil war veteran who explored the canyon and climbed its walls. Indeed, Glen Canyon was named by Powell. “So, we have a curious ensemble of wonderful features--carved walls, royal arches, glens, alcove gulches, mounds and monuments. From which of these features shall we select a name? We decide to call it Glen Canyon." (Major John Wesley Powell, 1869) Construction of the dam began in 1956. It was completed in 1962, but the lake did not completely fill until 1980.
Glen Canyon, slides 5-6 here
The dam itself is a thick arch dam, three hundred feet thick at the base, tapering to 25 feet thick at the top, and 710 feet tall. Construction used 4,901,000 cubic yards of concrete. At full capacity, it holds 27,000,000 acre-feet of water. It is on the Colorado River in north-central Arizona, about 15 miles upstream of Lee’s Ferry and 12 river miles downstream of the Arizona-Utah state line. The dam is the 4th highest dam in the country and 22nd highest in the world.
It became one of the most controversial areas in the National Park system. That status has not changed, and there are many who advocate tearing down Glen Canyon Dam. Indeed, a few want to do so by force, although this would cause incredible damage downstream. Over forty years later, a 1997 proposal to restore Glen Canyon (see Glen Canyon Institute for more information) by at least partially draining Lake Powell gained much media attention. Proponents value and want to restore the incredible beauty of the Glen's canyons-sinuous, towering sandstone walls, and lush hanging gardens-that disappeared under Lake Powell.
As word of this controversial proposal spread, opposition formed quickly. Opponents champion the value of Lake Powell's water storage, power generation, and lake-oriented recreation as reason to save Lake Powell. Both sides raise numerous compelling issues about the relationship between humans and the land, and about what our relationship with nature should be.
Glen Canyon, slides 7-8 here
The oldest exposed rocks in Glen Canyon National Recreation Area date from the Pennsylvanian and Permian periods of the late Paleozoic Era, and these are visible only in a few places. The oldest is the Paradox Formation, which is seen as pinkish-gray vertical and irregular cliffs. Most of this rock was deposited underwater. It can be seen in Cataract Canyon and in the depths of the upper San Juan River Canyon. The Permian Period rocks, which consist of the Cutler, Cedar Mesa, and Honaker Trail formations, are beachlike deposits. They form pinkish to gray-colored irregular cliffs and ledges in Glen Canyon. These formations can also be seen in Cataract Canyon of the Colorado River and in San Juan River Canyon.
The Triassic Period (248 to 205 MYBP) began with the deposition of fine-grained, reddish-brown sandstone known as the Moenkopi Formation. Ripple marks and mud cracks are evidence that this region was a tidal mud flat, with ancient tides and occasional floods. Orogenesis caused the area to tilt slightly, with some volcanism. The resulting Chinle Formation is made up of multicolored beds of volcanic ash, oozes, and silt. The Moenkopi Formation and the Chinle Shale can be seen at Lees Ferry and the Rincon. As the inland sea began to recede, the region's climate changed, and it became a desert. Windblown sand drifted in, creating the Wingate Sandstone.
The Jurassic Period began 206 million years ago, creating the bold cliffs and ledges of the Kayenta Formation, notable for their black and gunmetal-blue streaks of color or "desert varnish." During this point in geologic time, another series of formations was created.
Glen Canyon, slide 9 here
The Morrison Formation consists of sandstone, limestone, and mudstone deposited by rivers flowing into the area. The Entrada Formation, which is made of Entrada Sandstone, appears in the Wahweap area as white-colored rock, though it is more commonly a creamy-yellow color. The Morrison and Entrada formations make up Castle Rock and Tower Butte. The Carmel Formation, with its flat, maroon-purple-brown beds, is seen along Lakeshore Drive, between Glen Canyon Dam and Wahweap. The red, orange, or white Navajo Sandstone (which forms Rainbow Bridge) is the most common type in Glen Canyon NRA.
Glen Canyon, slide 10 here
The stratigraphic sequence is shown on slide 10.
Glen Canyon, slide 11 here
Navajo sandstone forms the canyon walls at the damsite and throughout most of the reservoir basin. The sandstone is remarkably uniform and homogeneous over wide areas and nearly identical samples can be obtained from areas separated by many miles. The Navajo sandstone is buff to reddish, medium to fine-grained, and moderately hard to soft. It is massive with pronounced cross-bedding and commonly indistinct horizontal bedding. The sandstone is moderately porous and highly absorptive, owing to the high capillarity created by the small size of intergrain pore spaces.
Creation of the Canyon
Glen Canyon formed because of raging waters that pass through it, rather than the foundation upon which it was carved. The Colorado and San Juan Rivers are the agents. When these rivers formed and how they carved the canyon is a controversy that may never be settled. John Wesley Powell, in the late 1800's, suggested that the rivers preexisted the rise of the plateau (60-100 mybp). During uplift, the rivers cut downward rapidly, remaining at the same level, thus carving Glen Canyon as it was prior to 1963.
Some have argued that the Colorado and San Juan are low-energy, meandering rivers. It would have been impossible for such waterways to dissect more powerful rising landscapes. The "superposition theory" suggests that the basins between Tertiary uplifts and folds were eventually filled in by sediments. This allowed low-energy meandering rivers to traverse what would have been a flatter landscape. The rivers therefore followed the plateau uplifts (Baars, 2000).
Modern theories support an extremely fast erosion of Glen Canyon as recent as 5 million years ago. Whenever and however the Glen Canyon was carved, one fact is undeniable: its primary erosive agents were the Colorado and San Juan Rivers. The deepening of the canyon was caused by the abrasive action of transported sediments in the rivers. The widening of the canyon was the result of several processes: freeze-thaw weathering of the canyon walls, torrential rains which caused wash-outs and sediment-laden landslides, and anthropogenic influences (Baars, 2000).
Glen Canyon, slide 12 here
Since the filling of Lake Powell, new problems have developed. One is the rapid increase in use by boats on Lake Powell. About 2.000,000 people nights are spent on the beaches of Lake Powell. It is akin to a small city. These people use clean water, produce sewage and garbage, and may spill gasoline or petroleum into lake waters. At times, this has lead to an increase in fecal coliform bacteria counts along beaches.
Glen Canyon, slide 13 here
Another problem is graffiti. GRIT is the Graffiti Removal and Intervention Team. There job is to remove existing graffiti and try to prevent additional graffiti. With the abundance of soft rocks, the graffiti often includes carvings in the rock.
Glen Canyon, slide 14 here
All My Rivers are Gone, Katie Lee, Johnson Books, Boulder, Colorado, 1998.
Cadillac Desert, Marc Reisner, Penguin Books, New York, 1986.
The Exploration of the Colorado River and Its Canyons (formerly titled Canyons of the Colorado), John Wesley Powell,Viking Penguin, 1997.
The Colorado Plateau, Donald Baars University of New Mexico Press, revised, 2000).
The Story that Stands Like a Dam: Glen Canyon and the Struggle for The Soul of the West, Russell Martin, Henry Holt, New York, 1989.
A World Wide Web tour of Glen Canyon.
City of Page, Story about the city of Page, Arizona, a town created to support the construction of Glen Canyon Dam and powerplant.
Deciding what kind of river we want, by George Sibley, High Country News, v. 28, #13, 7/22/1996.
Glen Canyon Institute.
Glen Canyon Odyssey, Phil Pennington, Narrative and photos about Glen Canyon.
Glen Canyon: Using a dam to heal a river, by George Sibley, High Country News, v.28, #13, 7/22/1996.
Grand Canyon Explorer, The Powell Expedition, Log of Powell’s expeditions from his books.
Images of Glen Canyon, Phil Pennington.
Images of Glen Canyon, C. Gregory Crampton
Katie Lee, excerpts from her writings.
Map Showing Quaternary Geology and Geomorphology of the Lees Ferry Area (Text), Glen Canyon, Arizona By Richard Hereford, Kelly J. Burke, and Kathryn S. Thompson (Map will be posted in classroom)
Major John Wesley Powell, short biographical sketch for the John Wesley Powell Memorial Museum.
Memories, a scrapbook of enchanted places, from the memories of Phil and Keturah Pennington, illustrated with photos of Glen Canyon.
Navigating Glen Canyon, links to other resources concerning Glen Canyon.
Reclaiming a lost canyon, by Greg Hanscom, High Country News, v.29, #21, 11/10/1997. Information about some of the early opponents of Glen Canyon Dam, including Phil Pennington and Katie Lee.
United States Geological Survey current streamflow data for Glen Canyon dam. Note: The gaging station is 16 miles downstream from the dam, but there are no discharges between the dam and the gaging station.
Virtual Tour of Glen Canyon, Glen Canyon Institute.
Link is to the official National Park Service site - many parks have additional web sties with worthwhile information
Glen Caynon NRA
© 2005 by David L. Warburton
Questions or comments? mailto:email@example.com
Last updated: May 16, 2005