# Mascall Formation

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Geological formation in Oregon, United States

Mascall Formation Stratigraphic range: Hemingfordian-Barstovian ~20.4–13.6 Ma PreꞒ Ꞓ O S D C P T J K Pg N Outcrop near Picture Gorge Type Sedimentary Underlies Rattlesnake Formation Overlies John Day Formation Area John Day Valley, Fox Basin Thickness 2,000 feet (610 m) Lithology Primary Sandstone, conglomerate Location Extent eastern Oregon Type section Named for Mascall Ranch (south of Dayville) Named by J. C. Merriam Year defined 1901[1]

John Day Fossil Beds map

The **Mascall Formation** is a [Miocene](/source/Miocene) [geologic formation](/source/Geologic_formation) found along the [John Day River Valley](/source/John_Day_River) of [Oregon](/source/Oregon), in the [Western United States](/source/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](/source/Sandstone), ash, light colored water-laid [tuff](/source/Tuff), and well-rounded [conglomerate](/source/Conglomerate_(geology)). Within the Mascall Formation is a widespread [ignimbrite](/source/Ignimbrite) unit which consists of 97 to 99 percent glass shards and minor amounts of [anorthoclase](/source/Anorthoclase), [quartz](/source/Quartz), [magnetite](/source/Magnetite), [zircon](/source/Zircon), and [clinopyroxene](/source/Clinopyroxene)."[2][3]

## Age

The ignimbrite was [radiometrically dated](/source/Radiometric_dating) at 13 million years.[2] Parts of the Mascall are interfingered with the [Columbia River Basalt Group](/source/Columbia_River_Basalt_Group).

## Fossils

[Barstovian](/source/Barstovian) [vertebrates](/source/Vertebrate) have been recovered from the Mascall.

## References

1. **[^](#cite_ref-1)** Merriam, J. C., 1901. A contribution to the geology of the John Day Basin, Oregon: Univ. Calif., Dept. Geol. Sci. Bull., v. 2, p. 269-314.

1. ^ [***a***](#cite_ref-GFOEO_2-0) [***b***](#cite_ref-GFOEO_2-1) *Geologic Formations of Eastern Oregon* (East of longitude 121°30'), 1972. John D. Beaulieu. [Bulletin 73](http://www.oregongeology.org/pubs/B/B-073.pdf). Oregon Department of Geology and Mineral Industries.

1. **[^](#cite_ref-3)** Davenport, R. E., 1970. *Geology of the Rattlesnake and older ignimbrites in the Paulina Basin and adjacent area, central Oregon*: [Oregon State University](/source/Oregon_State_University) doctoral dissertation, 132 p., unpublished.

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