and very clean sandstone with well-rounded, generally very fine-grained and frosted sand. It reached its greatest thickness, 2,000 feet (610 m) in what is now Zion National Park (see geology of the Zion and Kolob canyons area). The cross-bedded make-up of the Navajo leads to the formation of curvilinear canyons and rounded domes such as Capitol Dome and Navajo Dome. In other places it forms massive cliffs and monoliths. Subsequent erosion leveled the tops of the sand dunes and left them in up to 60 foot (18 m) thick easy to discern layers. San Rafael Group (Jurassic) Frequent but short-lived changes in sea level during the Mid to Late Jurassic periodically flooded the area with shallow extensions of the ocean. The resulting San Rafael Group is composed of four formations that were deposited on top of the Glen Canyon Group's regionally traceable erosion surface. San Rafael Group formations are (from oldest to youngest); Page Sandstone, Carmel Formation, Entrada Sandstone, Curtis Formation, and Summerville Formation. San Rafael formations can be seen on the east-dipping part of the Waterpocket Fold. Climatic conditions were still arid when the locally 0 to 100 feet (0 to 30 m) thick Page Sandstone was deposited above the reach of high tide yet near the shore of an advancing sea (sabkha-like conditions). This formation is composed of three members; the Harris Wash, Judd Hollow, and the Thousand Pockets. Together they were laid on top of the Navajo sand dunes as the sea slowly flooded the vast desert. An outcrop of the Judd Hollow Member can be seen from mile marker 86.5 as a red cliff above the Fremont River falls. The cross-bedded sandstone just above the red cliff is an example of the Thousand Pockets Member. In Mid Jurassic time gypsum, sand, and limey silt were deposited in what may have been a graben that was periodically covered by sea water and thus a place where repeated flooding was followed by evaporation. The resulting Carmel Formation is composed of 200 to 1,000 feet (60 to 300 m) of reddish-brown siltstone, mudstone and sandstone that alternates with whitish-gray gypsum and fossil-rich limestone in a banded pattern. Fossils include marine bivalves and ammonites. Most of the Carmel has been removed from the Waterpocket Fold's crest but outcrops can be seen capping the Golden Throne and atop various domes in the area. It can also be seen as reddish-brown triangular-shaped