Mascall Formation
The Mascall Formation is a Miocene geologic formation found along the John Day River Valley of Oregon, in the Western United States.

Description
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."

Age
The ignimbrite was radiometrically dated at 13 million years.  Parts of the Mascall are interfingered with the Columbia River Basalt Group.

Fossils
Barstovian vertebrates have been recovered from the Mascall.

References

Geology of Oregon
Neogene geology of Oregon
Sandstone formations of the United States
Tuff formations