Wednesday, March 16, 2011

The Cutler divided and undivided

Back in the Permian the Uncompahgre Mountains in western Colorado were experiencing extensive erosion and creating some great alluvial fans to the west all the way into now what is Utah. These red beds, now called the Cutler formation after a small creek just north of Ouray CO can be seen from western Colorado into central Utah. What is interesting is that the Cutler seems to have two sets of identities. In western Colorado, extreme eastern Utah and other places along the Colorado River we find the Undivided Cutler.

The undivided identity is a thick mix of irregular collection of dark red, lumpy sandstones, mudstones and conglomerates.

The divided sequence looks a little different. It too has the debris from the Uncompahgre Mountains but it also shows a more complex geologic story. The earliest layers show a shale/limestone mix complete with fossils indicating a marine origin. Resting above the limestone is the Cedar Mesa Sandstone an inter-fingering of near beach white sandstone and the red from the Uncompahgre Mountains showing a changing sea level. The sequence is finally topped with a brilliant white aeolian sandstone showing again a very different environment.

Taken from the Colorado River overlook. The Undivided Cutler in the foreground with the Needles of the Cedar Mesa Sandstone of the divided Cutler in the background.

A closer look at the Undivided Cutler looking down at the Colorado River

1 comment:

Malcolm V L said...

Is it just me or is there some fault displacement evident in the upper slanted layers?