Arroyo Formation
| Arroyo Formation | |
|---|---|
| Stratigraphic range: | |
| Type | Formation |
| Unit of | Clear Fork Group |
| Underlies | Vale Formation |
| Overlies | Waggoner Ranch Formation |
| Thickness | 250 ft (76 m) |
| Lithology | |
| Primary | Limestone, mudstone |
| Other | Gypsum |
| Location | |
| Coordinates | 33°48′N 99°12′W / 33.8°N 99.2°W |
| Approximate paleocoordinates | 0°24′N 29°36′W / 0.4°N 29.6°W |
| Region | Texas |
| Country | United States |
| Type section | |
| Named for | Los Arroyos, Runnels County, Texas |
| Named by | Beede & Waithe |
| Year defined | 1918 |
The Arroyo Formation, sometimes termed the Lower Clear Fork Formation, is a geologic formation in Texas. It preserves fossils dating back to the Kungurian stage of the Permian period. It is the lower-most portion of the Clear Fork Group, part of a series of fossiliferous Permian strata in the south-central United States known as the red beds.