a carbonate platform environment, with few distinct fossil assemblages. Although thickest in the west, Devonian strata are present in the east unlike Ordovician and Silurian rocks. A local orogeny produced the Stansbury Uplift, leading to downward erosion into older rock units dating to the Precambrian and the deposition of the coarse conglomerate Stansbury Formation. Shale and quartz sandstone are often interbedded with carbonates as in the Hanauer Formation in the Thomas-Dugway Range. In the Mississippian, up to of sediment accumulated in the Oquirrh Basin. Marine deposition was continuous, with numerous fossils in an unbroken record, such as the crinoid stems, brachiopods and corals in the Chainman-Manning Canyon shale. Silicified brachiopod and coral fossils mark the Redwall, Leadville, Madison, Gardison, Joana and Lodgepole limestones and only the northwest lacks extensive limestone formations. Geologists focused significant attention on the Pennsylvanian rocks of the Paradox Formation in the Paradox Basin after the discovery of oil, potash and rock salt. The basin took shape as part of the Uncompahgre Uplift, produced by the uplift of the ancestral Rocky Mountains. Several thousand feet of salt accumulated beneath arkose shed off the mountains. Up to 13,000 feet of sedimentary rocks accumulated in the Oquirrh Basin. A small unconformity separates these rocks from those formed in the Permian. These rocks tend to be difficult to correlate, with significant lateral variation, cross-bedded sandstones indicating wing transportation and a lack of late Permian rocks. A major marine transgression generated the Kaibab Limestone (the rimrock of the Grand Canyon), represented by the Park City and Phosphoria groups in Utah. Mesozoic (251-66 million years ago) In the early Mesozoic, one final marine deposit formed in western Utah during the Triassic—the Thaynes Limestone—before the region was uplifted. The early Triassic Moenkopi Formation is a mudstone with thin layers of limestone formed as the sea spread out across mud flats and hosts the Canyonlands in southern Utah. From east to west, mudstone grades into limestone. The Navajo, Wingate and Kayenta sandstones are distinguished by the cross-bedding of the Kayenta Sandstone across the Colorado Plateau, which tends to be more characteristic of a stream environment than the sand dune deposits that make up the Wingate Sandstone. The Navaja Sandstone began to form in the late Triassic, but is mainly a Jurassic formation, including the formations in Zion National Park. Other important Jurassic units include the Entrada Sandstone, which hosts Arches National Park and the