[1][2] The Canutillo Formation consists of about 15 feet (4.6 m) of soft gray siltstone.

Fossils include abundant Leiorhynchus and other brachiopods and a few pelecypods.

[1] The formation was first described in his dissertation by L.A. Nelson in 1937 for outcrops in the Franklin Mountains.

[3] Nelson formally published the definition in 1940 and extended the outcrop range to the Hueco Mountains.

[5] In 1949, Lowell R. Laudon and Arthur L. Bowshwer restricted the formation to a sequence of just 15 feet (4.6 m) of soft gray siltstone.