Conor Watkins And J. David Rogers
Grand Canyon Research
Cogswell Butte Landslides And River Diversions

Cogswell Butte as it appears from the Esplanade.  This butte is mantled with small landslides and talus on the northern side but spawned several megalandslides on its southern side.  Surprise Valley is located between the Esplanade and Cogswell Butte.

The Cogswell West Landslide is located on the southwestern margins of Cogswell Butte and was probably one of the earliest slides to dam Deer Creek.  At that time Deer Creek was divereted west of its present course.  The slide breccia is cemeted by travertine and appears to predate most other events in this corridor.  Isolated patches of slide debris mantle the Canyon wall on the opposite (south) side of the Colorado River, suggesting this slide may have once dammed the Colorado River. 

The oldest channel of Deer Creek is exposed along the river trail about 500 m east of Deer Creek and approximately 100 m above the Colorado River.

The West Cogswell Landslide contains an internal structures typical of translational block glide landslides, including numerous grabens, like the one shown here.

The Base of the Bright Angel Shale within the West Cogswell Slide mass exhibits a series of kink bands or chevron folds, as seen here.  These are suggestive of basal compression and overriding of the upper slide mass, suggestive of slow movement.

A  wide angle view of the chevron folds exposed along the base of the West Cogswell Slide.  These structures are in variance with the cemented breccia zones we usually observe along the base of megalandslides in the this part of the Grand Canyon.

The chevron folds carry upwards of 150 feet through the remnants of the West Cogswell Slide, which is highly dissected and denuded.

The basal rupture surface of the West Cogswell slide is exposed along the upper river trail between Deer and Tapeats Creek, seen here.  Scrub vegetation in this area appears to be fed by intermittent springs issuing from the toe of the old slide.

The Cogswell East Landslide as viewed from the Deer Creek Landslide to the west.  This slide consists of two large backrotated blocks, with the lowest one damming the Colorado River.  This event diverted the river to a near course where it began downcutting through Precambrian granites, creating what is known as the Granite Gorge of the Colorado River.  The unofficial narrowest point of the Colorado River in the Grand Canyon is located here when the water is low.

Conor overlooks the Granite Narrows from the Deer Creek Slide.

A closer view of the Granite Narrows shows the incised channel of the Colorado River, which reaches a depth of 85 feet with a width as little as 76 feet.  The water turns brown with sediment in the late summer and fall during the rainy season. 

Rafters floating through the Granite Narrows.

The two massive backrotated blocks of the Cogswell East Landslide are classic examples of Toreva blocks.  This view is looking east from the Deer Creek Landslide. 

Close-up view of the upper slide block of the East Cogswell Landslide.

Ancient channel of the Colorado River filled by the East Cogswell Slide at Mile 135, as it appears from river level, just upstream.  The slide debris fell on top of channel gravels and a series of clastic dikes punctuate the slide debris, indicative of hydraulic fracturing.

Desert big horn sheep are commonly seen along the river trail in the vicinity of the Mile 135 buried channel. 

Another view of the big horn sheep, including some youngsters, walking in single file along the lower river trail.

The official narrowest point on the Colorado River is located just upstream of the Granite Narrows and is only 76 feet across.

A closer view ot the narrowest point along the Colorado.  Notice the sediments deposited behind this constriction during high water.

In 1978 Dave Rogers and Marvin Pyles, grad students at U.C. Berkeley, began studying massive landslides in the Grand Canyon region.  They hired a private aircraft to take stereopair images of landslide features throughout the canyon, sometimes from as low as a few hundred feet!  They noticed two slumps enamating from the southern side of Cogswell Saddle, shown above.  These are not visible when traversing the River Trail between Deer and Tapeats Creek but might be viewable from the south side of the Colorado River.

A similar view of the Cogswell Butte created using Terragen, a photorealistic scene generator that uses digital elevation models (DEMs) to render scenes.  Note the similarities between the prototype scene and the artificial rendering.  This image was generated using a 10 meter DEM.  Although the resolution is only 10 m, renderings can be useful forensic tools to ascertain where old photographs were imaged.  Images depicting the Martian landscape using Terragen appeared on the cover of the January 2004 National Geographic Magazine.

Questions or comments on this page?
E-mail Dr. J David Rogers at
or Conor Watkins at