Friday, November 21, 2008

Decorative rock and the Cutler formation

My next door neighbor, a retired local rancher invited me over to check out his new boulder. His ranch is in the valley below a great outcrop of Cutler and he decided that this conglomerate needed to be in his retirement from yard. His real reason for inviting me over was to give a quick historical geology lesson about the origins of his boulder.

The Cutler, at least here in Western Colorado is a rough conglomerate filled with the practically unsorted material that eroded off of the Ancestral Rockies...or at least here the Ancestral Uncompahgre Plateau. If my photo taking skills were better, you would be able to see largish cobbles (I did remember to add a nickle for scale) of all sorts showing the type of rocks that made the highlands of the Pennsylvanian. We discussed how you could break off a larger cobble and hold in your hand a chunk of rock from an ancient mountain range. He was impressed that he took the boulder from the location that gives its name to the formation. Cutler Creek.

Coupled with the Fountain formation, Minturn formation and the Maroon formation (all contemporaries, all red beds and all conglomerates) we see the outlines of the Ancestral Rockies during the Pennsylvania and Permian periods. This has been a great exercise with my students in trying to determine the extent of this ancient mountain range from data easily dug up today. They can visualize the high energy environment that mimics what we see in the mountains today creating these alluvial fans of conglomerate.

1 comment:

Silver Fox said...

The large cobbles show up well in those photos when enlarged. Quite a variety of rock types!