The mudstone and siltstone beds weather to yellow, are rich in mica, and are not resistant to erosion.

[1] In addition, river channel deposits in the Raton Formation are up to six times wider and five times deeper than river channels in the Poison Canyon Formation, and the channels in the Poison River Formation tend to be isolated and lack any sheet-like amalgamation.

[6] The Poison Canyon Formation contains sparse fossilized plant remains characteristic of the Paleocene.

[7] The formation is a significant freshwater aquifer in the Canon City, Colorado area.

Hills later clarified the definition, separating the uppermost beds of his measured section to the Huerfano Formation.