The Thirtynine Mile volcanic area, part of the larger Central Colorado volcanic field, is an extinct volcanic area located in Park and Teller counties, Colorado, northwest of Cripple Creek and southeast of South Park. The area was the site of significant volcanism in the Paleogene Period about 35 million years ago. Ashfall and lahars (mudflows) from the volcanoes created the conditions for fossilization at what is now Florissant Fossil Beds National Monument.
The Kneeling Nun Tuff is a geologic formation exposed in southwest New Mexico. It has a radiometric age of 35.3 million years, corresponding to the latest Eocene epoch.
The Mogollon-Datil volcanic field is a large silicic volcanic field in western New Mexico. It is a part of an extensive Eocene to Oligocene volcanic event which includes the San Juan volcanic field in southwestern Colorado, the Trans-Pecos volcanic field in west Texas and north central Mexico, the Boot Heel volcanic field in the bootheel of southwestern New Mexico and adjacent areas of Arizona and Mexico; and the vast volcanic field of the Sierra Madre Occidental of western Mexico. The Mogollon-Datil volcanic field was formed in "four discrete pulses representing synchronized activity of two separate cauldron complexes".
The Abiquiu Formation is a geologic formation found in northern New Mexico. Radiometric dating constrains its age to between 18 million and 27 million years, corresponding to the late Oligocene to Miocene epochs.
The Gila Group is a group of geologic formations found along the upper tributaries of the Gila River in Arizona and New Mexico. Radiometric dating of lava flows within the group yields an age of Miocene to Quaternary.
The Popotosa Formation is a geologic formation in New Mexico. It preserves fossils dating back to the Neogene period. These include the Socorro flora, notable for its fine preservation of plant reproductive structures.
The Baca Formation is a geologic formation in southern New Mexico and Arizona. It preserves fossils dating back to the Eocene period.
The Hart Mine Formation is a geologic formation controversially defined from exposures in south-central New Mexico. It preserves fossils dating back to the Eocene epoch.
The Palm Park Formation is a geologic formation in southern New Mexico. It preserves fossils dating back to the Eocene epoch.
The Rubio Peak Formation is a geologic formation in southwestern New Mexico. It is thought to have been deposited in the Eocene Epoch.
The Santa Fe Group is a group of geologic formations in New Mexico and Colorado. It contains fossils characteristic of the Oligocene through Pleistocene epochs. The group consists of basin-filling sedimentary and volcanic rocks of the Rio Grande rift, and contains important regional aquifers.
The Tanos Formation is a geologic formation in central New Mexico. It is estimated to be about 25 million years in age, corresponding to the Oligocene epoch.
The Keres Group is a group of geologic formations exposed in and around the Jemez Mountains of northern New Mexico. Radiometric dating gives it an age of 13 to 6 million years, corresponding to the Miocene epoch.
The Spears Group is a group of geologic formations exposed in and around the northeast Mogollon-Datil volcanic field of southwestern New Mexico. It has a radiometric age of 33 to 39 million years, corresponding to the Eocene to Oligocene epochs.
The Hayner Ranch Formation is a geologic formation found near the San Diego Mountains of New Mexico. It is estimated to have been deposited during the Miocene epoch.
The Love Ranch Formation is a geologic formation in southern New Mexico. It was likely deposited during the late Paleocene and early Eocene epochs.
The Oligocene Chuska Sandstone is a geologic formation that crops out in the Chuska Mountains of northeastern Arizona and northwestern New Mexico. The formation is a remnant of a great sand sea, or erg, that once covered an area of 140,000 square kilometres (54,000 sq mi) reaching from the present locations of the Chuska Mountains to near Albuquerque and to the southwest. This erg deposited a succession of sandstone beds exceeded in thickness only by the Navajo Sandstone on the Colorado Plateau.
The Bearwallow Mountain Andesite or Bearwallow Mountain Formation is a geologic formation exposed in and around the Mogollon Mountains of southwest New Mexico. It has a radiometric age of 27 to 23 million years, corresponding to the late Oligocene to early Miocene epochs.
The Fence Lake Formation is a geological formation in western New Mexico whose strata were deposited in the Miocene.
