Monday, March 26, 2012

Geo-anatomy of a race course

Last weekend I had the chance to run in the Canyonlands 1/2 Marathon in Moab UT. Except for the wind (It is March in the desert after all) the race was lots of fun with geology at every side. The course follows the Colorado River as it flows south towards Moab.

At the start of the course, you can clearly see many of the typical Canyonland area rock units. Starting at river level is the ever popular Chinle formation of the Triassic period. This area was a large floodplain receiving material from the Uncompaghre uplift to the east. The Chinle is most famous for its uranium ore heavily mined during the 1950's.

Above the Chinle is my personal favorite: the Wingate sandstone. This Triassic aged cliff forming formation- former sand dune is ubiquitous through the Canyonland area. Its reddish hues catch that morning light just right to make the best campsites. Making a region-wide cap rock above the Wingate is the Kayenta formation containing lots of sandstone but also beds of shale and limestone showing a change in climate from sand dunes to at least occasional stream flows.

Another stratigraphic column shot from along the race course.
As the course makes its way to Moab, the late-Triassic Navajo sandstone makes an appearance atop the Kayenta formation. This shows yet another energy regime change away from the streams of the Kayenta to yet another huge sand dunes mass like the Wingate. This image also shows some structure with the ledges of the Kayenta dipping down into the river marking the edges of the Courthouse syncline.
The course doesn't end when the Colorado River reaches the Moab fault and the collapsed salt valley that created the valley where the town sits, there are still over two uphill miles into town left to go.
Over all a very fun run on a most beautiful course.