[3] The Tropic Shale outcrops in Kane and Garfield counties, with large sections of exposure found in the Grand Staircase–Escalante National Monument.

The Tropic Shale is predominantly marine mudstone and claystone, with several radioisotopically-dated bentonite marker beds, and occasional sandstone layers deposited during the late Cretaceous Period during the Upper Cenomanian through the Middle Turonian (95-92 Ma).

The contact with the overlying Straight Cliffs is gradational with the distinction between the two units defined as the point where sandstone becomes more abundant than shale.

The Tropic Shale has two dominate lithologies, with the lower two thirds of the formation consisting of a bluish gray calcareous mudstone that encompasses eleven ammonoid biozones, and the upper third that is a darker gray and non-calcareous that encompasses only one or two ammonoid biozones.

Additionally the upper portion, hummocky cross stratified and turbiditic sandstone beds become more common.

Rudists and solitary corals seem to be quite rare and have not been studied due to their lack of presence in the Tropic Shale as they are recorded from other formations associated with the Western Interior Seaway.

Studies have been done on the marine reptiles to determine the impact of OAE II on the biodiversity of the group in the Western Interior Seaway.

Results from that study seem to suggest that at least locally the OAE II had little to no effect on marine reptile diversity.

[13] Cold hydrocarbon seep bioherms in the lower portion of the Tropic Shale during the Cenomanian give glimpses of different ecosystems to the marine shelf deposits.