J. David Rogers'
Overview of PhD Research
Arches National Park

The natural arches at Arches National Park near Moab, Utah were a source of curiosity that entranced me.  I wondered how were they formed?  The ranger’s explanation of "wind erosion" seemed hopelessly naive.

The longest span at Arches is Landscape Arch, shown here.  It stretches 291 feet across, just about the length of a football field.  In 1973 Steve Tetreault and I managed to climb out onto it, finding it narrows to just 6 feet wide!  Climbing on the arch is no longer permitted.

View of Landscape Arch from upslope, showing the precipitous neck we tried to cross when we climbed onto the arch! The dumb things young men do....

Detail view of the prolific exfoliation exposed in the opening of Wall Arch at Arches Park.  To me, the exfoliation joints seemed responsible for the openings, not wind erosion.

While exploring the Grand Canyon I also came across numerous examples of profuse exfoliation, especially in the Esplanade Sandstone, shown here in North Canyon, a tributary of Marble Canyon.

Arches Park is unique in the development of lenticular sandstone "fins" developed within the Slickrock and Dewey Bridge members of the Entrada sandstone.  These were formed by the dilation as an enormous salt diapir pushed itself up along the axis of Salt Creek, northwest of Moab, Utah.

Ground view of a single fin at Arches Park.  They were aligned in a northwest-southeast azimuth, parallel to the Salt Creek diaper, which subsequently dissolved, causing the valley to collapse on itself.

In September 1977 I began mapping and sampling in Arches National Park, in anticipation of the project becoming the focus of my doctoral studies at Berkeley.

In the beginning I focused on obtaining representative specimens from each of the beds above, within and immediately beneath most of the prominent arches. I spent the month of December 1977 mapping and sampling.

In most of the arches I examined the degree of fracturing varied markedly between the three beds bounding the openings.  Here I am sampling a bed in the Slickrock member which exhibits little secondary fracturing, while the bed I am standing on exhibits profuse fracturing.

The work at Arches Park involved a lot of rock climbing, but without any permanent aids (no pitons were allowed).  The Park Service was very cooperative and supportive of academic research in those days.  You can barely make me out up on the cliff in this Dec 1977 view (arrow).

This is what things looked like up on the cliff face pictured above.  I am mapping “secondary joints”; the term I gave to those joints that form in response to topography and erosion, separate and distinct from regional systematic joints, which pervade every rock mass.

One of the most intriguing aspects of cliff morphology in the Colorado Plateau is the influence of discrete shale seams on cliff morphology. This view shows me sampling a one-inch thick shale seam next to Skyline Arch.  Most of these seams were severely slickensided.

One of the most unusual features I mapped at Arches Park were these enormous paleoliquefaction structures, which looked like gigantic sand boils, petrified in time.  20 years later Walter Alvarez at U.C. Berkeley explained these as the result of a nearby meteorite impact during the Jurassic Period. I mapped similar features in upper Lake Powell, though more subdued.

Questions or comments on this page?
E-mail Dr. J David Rogers at rogersda@mst.edu.