The formation is described in Geologic Formations of Eastern Oregon (1972) as follows: The unit is composed of up to 700 feet of fanglomerate and finer terrestrial sediments and a 40-foot thick ignimbrite unit which crops out in the middle of the section.

The ignimbrite displays zonation typical of welded ashflow tuffs and is a prominent ridge former.

[2]The ignimbrite was radiometrically dated by the Potassium–argon method at 6.4 million years by Evernden and James (1964).

Fossils found here include Amebelodon sp., the extinct peccary Mylohyus longirostris, the extinct North American rhino Teleoceras fossiger, Indarctos oregonensis, Pliohippus spectans, Machairodus sp., Hemiauchenia vera, an extinct species of fox known as Vulpes stenognathus and the earliest record of modern-day beavers.

[4][5][6] In the lower fanglomerate member of the Rattlesnake Formation, remains of Pekania occulta were found.