| Mascall Formation | |
| Type: | Sedimentary |
| Age: | Hemingfordian-Barstovian ~ |
| Period: | Langhian |
| Prilithology: | Sandstone, conglomerate |
| Namedfor: | Mascall Ranch (south of Dayville) |
| Namedby: | J. C. Merriam |
| Year Ts: | 1901[1] |
| Underlies: | Rattlesnake Formation |
| Overlies: | John Day Formation |
| Thickness: | 2000feet |
| Extent: | eastern Oregon |
| Area: | John Day Valley, Fox Basin |
The Mascall Formation is a Miocene geologic formation found along the John Day River Valley of Oregon, in the Western United States.
The formation is described in Geologic Formations of Eastern Oregon (1972) as follows: "The Mascall Formation consists of a maximum of 2,000 feet of fluvial sandstone, ash, light colored water-laid tuff, and well-rounded conglomerate. Within the Mascall Formation is a widespread ignimbrite unit which consists of 97 to 99 percent glass shards and minor amounts of anorthoclase, quartz, magnetite, zircon, and clinopyroxene."[2] [3]
The ignimbrite was radiometrically dated at 13 million years.[2] Parts of the Mascall are interfingered with the Columbia River Basalt Group.
Barstovian vertebrates have been recovered from the Mascall.