Capitol Reef's sedimentary rocks were uplifted as a monocline, a 'step-up' in rock layers. Erosion has created an impressive cross-section of 19 different rock formations. Ron Blakey. Geology - Capitol Reef National Park (U.S. National Park Service) The scenery of the Entrada Sandstone temples of Cathedral Valley is complemented by evidence of other geologic processes at work. The flowing and dissolving of gypsum, a soluble mineral from the underlying Carmel Formation, created Glass Mountain and the Gypsum Sinkhole. Glass Mountain is an exposed plug of gypsum. The Gypsum Sinkhole formed when a gypsum deposit dissolved. Dikes and sills, which are thin bodies of igneous rock and small volcanic plugs, are found in Upper Cathedral Valley. These features formed during volcanic activity three to six million years ago. For more on the geology of Cathedral Valley, see the main Cathedral Valley page. Learn more about the Fossils found in Capitol Reef. Discover other national park sites with unique geologic features.