The Organ Rock Formation or Organ Rock Shale is a formation within the late Pennsylvanian to early PermianCutler Group and is deposited across southeastern Utah, northwestern New Mexico, and northeastern Arizona. This formation notably outcrops around Canyonlands National Park, Natural Bridges National Monument, and Monument Valley of northeast Arizona, southern Utah. The age of the Organ Rock is constrained to the latter half of the Cisuralian epoch by age dates from overlying and underlying formations. Important early terrestrial vertebrate fossils have been recovered from this formation in northern Arizona, southern Utah, and northern New Mexico. These include the iconic Permian terrestrial fauna: Seymouria, Diadectes, Ophiacodon, and Dimetrodon. The fossil assemblage present suggests arid environmental conditions. This is corroborated with paleoclimate data indicative of global drying throughout the early Permian.
The Organ Rock Formation is present across southeastern Utah, U.S.A. It outcrops around Canyonlands National Park, Natural Bridges National Monument, and Monument Valley. In these areas the Organ Rock typically outcrops as a dark-red/brown siltstone to mudstone gently dipping towards the southeast. Within Canyonlands N.P. it forms towers which are meters to tens of meters tall. These are protected by caps of the White Rim Sandstone. In general, the Organ Rock Formation records the evolution of terminal fluvial fans, which dry up into sections of overlying formations. Animals living during the time of the Organ Rock’s deposition had the capacity to travel across most of earth’s landmass, as at the time, land was all concentrated into the supercontinent Pangea.
The Organ Rock Formation is conformably underlain by the Cedar Mesa Sandstone. It is conformably overlain by the De Chelly Sandstone around Monument Valley and by the White Rim Sandstone in the Canyonlands National Park. In locations where the De Chelly and White Rim are absent, the Organ Rock is unconformably overlain by the TriassicMoenkopi or Chinle Formations by an erosional contact. Toward its eastern extent, the Organ Rock Formation grades into the Cutler Formation, undivided. This transition occurs to the southwest of Moab, UT. The age of the Organ Rock Formation is unconfirmed. The preceding Cedar Mesa Sandstone is dated to the Wolfcampian (ICS stage: Artinskian). The anteceding De Chelly and White Rim Sandstones are dated to the Leonardian (ICS stage: Kungurian). These formations constrain the age of the Organ Rock Formation to the latter part of the Cisuralian Epoch, approximately 290.1 to 272.3 Ma. The Organ Rock Formation may contain the Artinskian/Kungurian boundary. This is during the early to mid-Permian, a time where synapsids and temnospondyl amphibians are the dominant players in terrestrial ecosystems. These animals predate the advent of archosaur reptiles which give rise to dinosaurs in the Triassic.