The hoodoos are composed of conglomerate, sandstone, and siltstone, the kinds of sediment associated with deposition by rivers and streams in alluvial fans and shallow lakes. The coarseness of the sediments suggests a local source area. A few light-colored ash layers in the sediments provide the opportunity to date the sediments.
In the last post, we discussed the eruption of the Joe Lott tuff, which took place 19 or so million years ago. Soon after the blasts, volcanism declined, and the region began to stretch. The onset of basin and range extension caused numerous fault valleys to develop, and these local basins started filling with sediments washed from the adjacent uplifted mountains. The layers at Castle Rock were laid down between about 14 to 5 million years ago, on top of the tuff deposits.
It was great place to explore! After a few hours we packed and hit the road, heading east on Interstate 70, wondering what would come next. The answer wasn't long in coming, but that's another post!
For more information on the geology at Castle Rock Campground, check out:
and chapter 12 of Geology Underfoot in Southern Utah, by Orndorff, Wieder, and Futey