Dinosaur National Monument - Crossbedding

The white sandstone hogbacks in the background of this view from the Split Mountain Overlook consist of Weber Sandstone (Pennsylvanian and Permian age). Crossbedding in the well-sorted white sandstone suggests eolian deposition, and interbeds of fossiliferous limestone indicate that some sediments accumulated in a coastal setting (Gregson and Chure, 2000). These strata have been uplifted by mountain-building episodes that affected a wide region. Now the Weber Sandstone is being eroded by streams and rivers. Two stream terraces are clearly visible in the foreground of this image: one is about 40 feet above the current river level and probably represents down cutting since the peak of the last major glaciation about 18,000 years ago. The higher, well-developed surface probably corresponds to an earlier major glaciation period in the Rocky Mountain region, possibly between 95,000 to 130,000 years ago (Chadwick and others, 1997). Elevated terraces like these can be seen along river and stream valley throughout the western states.