| Spears Group | |
|---|---|
| Stratigraphic range: Eocene to Oligocene | |
 Dog Springs Formation in the Sawtooth Mountains of New Mexico | |
| Type | Group |
| Sub-units | See text |
| Underlies | Fence Lake Formation Hayner Ranch Formation[1] |
| Overlies | Baca Formation |
| Thickness | 3,000 ft (910 m) |
| Lithology | |
| Primary | Volcaniclastics |
| Other | Andesite |
| Location | |
| Coordinates | 34°16′52″N 107°17′46″W / 34.281°N 107.296°W |
| Region |  New Mexico |
| Country |  United States |
| Type section | |
| Named by | Tonking |
| Year defined | 1957 |
  Spears Group (the United States)  Spears Group (New Mexico) | |
The Spears Group is a group of geologic formations exposed in and around the northeast Mogollon-Datil volcanic field of southwestern New Mexico.[2][3] It has a radiometric age of 33 to 39 million years, corresponding to the Eocene to Oligocene epochs.
- ^ Seager, W.R.; Hawley, J.W.; Clemons, R.E. (1971). "Geology of San Diego Mountain area, Dona Ana County, New Mexico" (PDF). New Mexico Bureau of Mines and Mineral Resources Bulletin. 97. Retrieved 14 August 2020.
- ^ Tonking, W.H. (1957). "Geologic map and sections of the Puertecito quadrangle, New Mexico". New Mexico Bureau of Mines and Mineral Resources Bulletin. 41. Retrieved 24 August 2020.
- ^ Osburn, G.R.; Chapin, C.E. (1983). "Nomenclature for Cenozoic rocks of northeast Mogollon-Datil volcanic field, New Mexico" (PDF). New Mexico Bureau of Mines and Mineral Resources Stratigraphic Chart. 1. Retrieved 25 August 2020.