a largely unbroken period of time and result from the specific depositional environment that the formation was laid down in. A member is a minor unit in a formation and a bed is a distinct subunit of a member. Groups are sets of formations that are related in significant ways such as, for example, all being deposited during a dry period that lasted millions of years or as the result of an ocean periodically flooding the same area over millions of years. The various kinds of unconformities are gaps in the geologic record. Such gaps can be due to a prolonged absence of deposition or due to subsequent erosion that removes previously deposited rock units. The following sections are ordered from oldest to youngest rock units in order to create a geologic history of events. This is the opposite order one would see in an actual cross section of the sediments because newer rock units are deposited on top of older ones per the law of superposition. Cutler and Kaibab formations (Permian) In early Permian time, Utah was on a continental shelf that was occasionally covered by a shallow arm of the Panthalassa Ocean. That part of Laurasia was on a passive continental margin not unlike the current west coast of equatorial Africa. The resultant formations are part of the approximately 290- to 250-million-year-old Cutler Formation (called a group locally) Utah was nearly on the paleoequator while the first members of the Cutler Formation were deposited but it had migrated nearly to 10° north latitude by around 275 million years ago. The Cutler records sedimentation during this time and is composed of four members (youngest to oldest): White Rim Sandstone, (resistant caprock) Organ Rock Shale (locally missing), Cedar Mesa Sandstone, and the Elephant Canyon (locally buried). Only the two sandstone members of the Cutler Formation, the Cedar Mesa and White Rim, are exposed in the park but they cannot be easily distinguished from each other and are thus often treated as a single stratigraphic unit there. The White Rim and Cedar Mesa are composed of fossilized cross-bedded sand dunes that were likely deposited in an arid coastal environment that periodically flooded with sea water. Sand in these formations are somewhat sorted by size, well-rounded (worn by abrasion), and range from very fine- to medium-grained. Good outcrops of the locally 800 foot (240 m) thick Cedar Mesa and 420 foot (128