the Colorado Plateau are: De Chelly Sandstone (Arizona, Colorado, New Mexico, Utah) — youngest White Rim Sandstone (Utah) Organ Rock Shale (Arizona, Colorado, New Mexico, Utah) Cedar Mesa Sandstone (Arizona, Utah) lower Cutler beds (Arizona, Colorado, New Mexico, Utah) — oldest Beds formerly assigned to the Elephant Canyon Formation, the Halgaito Shale, or the Rico Formation are included in the lower Cutler beds. The stratigraphy of the lower Cutler beds has long been controversial. Charles Whitman Cross and A.C. Spencer applied the name Rico Formation to beds in the Rico Mountains of southwestern Colorado that were transitional from the marine Hermosa Formation and the overlying continental Cutler Formation. These contained marine fossils suggesting the beds covered the Pennsylvanian to Permian time interval. The name came into wide use for transitional beds further west as petroleum geologists mapped the Colorado Plateau. However, the definition of the Rico was vague and it was mapped inconsistently in the region. This led Don Baars to recommend abandoning the Rico in favor of placing the upper, Permian beds in his new Elephant Canyon Formation and reassigning the lower, Pennsylvanian, beds to the underlying Honaker Trail Formation. However, other geologists objected to this because the contact was defined by the fusulinids present in the beds, which made this a chronostratigraphic rather than a lithostratigraphic distinction, and by a subtle angular unconformity that was not easily recognized in the field. This led to abandonment of the Elephant Canyon Formation and designation of all beds between the Honaker Trail Formation and the Cedar Mesa Sandstone as simply the lower Cutler beds. These also include beds previously assigned to the Halgaito Formation. In the Chama Basin of New Mexico, the Cutler Group has been divided into two formations: Arroyo del Agua Formation — younger El Cobre Canyon Formation — older A sandstone unit resembling the De Chelly Sandstone is present above the Arroyo del Agua Formation in the southernmost part of the basin, but in this region it is assigned to the Yeso Group. Extent Cutler outcrops are found in these geologic locations in Arizona, Colorado, New Mexico and Utah. Black Mesa Basin Paradox Basin Piceance Basin San Juan Mountains province San Juan Basin Uinta Basin History of investigation There is no designated type locality for the Cutler. It was named by Charles Whitman Cross and Ernest Howe in 1905 after Cutler Creek, which enters Uncompahgre River about 4