spurs called 'flatirons' that form the Waterpocket Fold's eastern rampart. A near-shore environment dominated by barrier islands, sand bars and tidal flats later returned to the region. The sand and silt deposited created the 400 to 900 foot (120 to 275 m) thick reddish orange Entrada Sandstone. Distinctive jointing systems in the Entrada lead to the formation of cathedrals and monoliths in Capitol Reef's Cathedral Valley, arches in Arches National Park and 'goblins' (the local name for hoodoos) in nearby Goblin Valley State Park. Entrada exposures in the southern part of the park are mostly made of flat-bedded siltstones and erode into slopes. Moving north, Entrada exposures increasingly become rich in cross-bedded sandstone and erode into cliffs with fewer and fewer slopes. Fine-grained sand and silt mixed with sandy lime were laid down as sediments on top of the Entrada Sandstone, forming the locally 0 to 175 foot (53 m) thick erosion-resistant Curtis Formation. A green iron potassium silicate called glauconite in the Curtis indicates it was deposited in a shallow sea. Outcrops of the light grayish-green Curtis can be seen as a capstone in the northern section of the park while it is locally absent in the southern part. Tidal flat conditions returned as the shallow sea that created the Curtis Formation retreated from land. Thin beds of reddish-brown mudstone alternating with less frequent beds of greenish-gray sandstone and limestone were deposited as sediments, forming the locally 50 to 250 foot (15 to 75 m) thick Summerville Formation. This formation erodes into ledgy cliffs and slopes and can be seen above Curtis caprock in Cathedral Valley. Fossilized mudcracks and ripple marks are found in the Curtis along with up to 28 foot (8.5 m) thick gypsum-rich beds. Morrison Formation (Jurassic) Again above sea level, streams laid down mud and sand in their channels, on lakebeds, and in swampy plains during the Upper Jurassic. This became the Morrison Formation, which is locally divided into three members (from oldest to youngest); Tidwell Member, Salt Wash, and Brushy Basin. The 50 to 100 foot (15 to 30 m) thick Tidwell Member is locally difficult to recognize and therefore may or may not be in the area's rocks. Easier to identify and study outcrops elsewhere in southeastern Utah indicate they were deposited in hypersaline lagoons. Clay, mud, silt, cross-bedded sand, and pebbles were later deposited by meandering streams and in flood plains, forming