The Cutler Formation or Cutler Group is a rock unit that is exposed across the U.S. states of Arizona, northwest New Mexico, southeast Utah and southwest Colorado. It was laid down in the Early Permian during the Wolfcampian epoch. Description At its type area north of Ouray, Colorado, the Cutler Formation consists of over of bright red sandstone, siltstone, and conglomerate beds alternating with reddish mudstone or clay-rich limestone. Further west, the unit shows great lithological diversity, and can be divided into easily recognizable mappable subunits. Here the Cutler is raised from formation to group rank and its subunits are themselves designated as formations. The unit in its type area remains at formation rank and is often described as the "undifferentiated Cutler". The formation overlies the Hermosa Group and is in turn overlain by either the Dolores Formation (near its type area) or the Moenkopi Formation (further west). It is laterally equivalent to the Abo Formation of central New Mexico, to which it seamlessly transitions in the Jemez Mountains. The formation has been dated to Wolfcampian near its type area. At this point in geologic time, the Uncompahgre Uplift of the Ancestral Rocky Mountains was still rising along an arc from eastern Utah through southwestern Colorado and into northern New Mexico. Tremendous quantities of sediment were eroded off the uplift and accumulated at its southwest margin to form the undifferentiated Cutler, which in some places reached a thickness of . Further west, eolian (wind), fluvial (river) and marine influences became important and produced the lithological variety of the Cutler Group. The undifferentiated Cutler consists of alluvial fan deposits in a narrow belt very close to the Uncompahgre Uplift, and fluvial deposits further out. The coarsest exposures are near Gateway, Colorado, within a mile of the thrust fault defining the southwest margin of the ancient Uncompahgre Uplift. Some granite boulders in these deposits are up to in diameter. However, thrusting along the uplift margin had ceased by the time the youngest beds were deposited. Further west, the formation transitions to thin (less than ) sandstone and conglomerate beds, in which the grains become finer towards the top of the bed (a fining upward sequence). These are interpreted as recording individual sheet flood events. Subunits The Cutler has been placed at either formation or group stratigraphic rank, depending on the publication. Its subunits, therefore, are variously called formations or members. Subunits on