Organ Rock Formation Organ Rock Formation The Organ Rock Formation or Organ Rock Shale is a formation within the late Pennsylvanian to early Permian Cutler 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. 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
Brazos Mountains the view from the west, including from Heron Lake. U.S. Route 64 crosses the southern end of the range at a 10,481 foot (3194 m) pass. Nearby are the photogenic Brazos Cliffs, headwaters of the Rio Brazos and part of the Rio Chama river system. These mountains overlook the Chama River, the largest tributary of the Rio Grande which lies to the east. In essence, these mountains are the southern extension of the South San Juan Range that lies in Colorado. The Brazos Mountains are the southwestern remnants of a Laramide peneplain resulting from the erosion of mountains formed 80