The presence of coaly shales and coals in the Hell Creek Formation of Montana suggests that there was a relatively high level of precipitation at the Cretaceous-Tertiary boundary.
The paleosol in the Hell Creek Formation at the end of the Cretaceous suggests a relatively high level of precipitation—up to 50 inches per year.
Abundant coal beds were deposited during the Middle and Late Cretaceous indicating that the climate had begun to warm and become much wetter.
Abundant coals and underclays in the Late Cretaceous suggest a warm, wet climate.
Cretaceous chalks such as the Niobrara Formation indicate a warming of sea surface waters that occured during a warming of the global climate.
Deeply rooted, light gray to tan clay soils (vertisol) in the Early Cretaceous suggest a seasonally wet, humid climate.
Gypsum deposits of the Jurassic Gypsum Springs Formation indicate salt deposition characteristics of an arid climate.
Abundant layers of carbonate nodules and scattered root traces indicate that the Late Jurassic Morrison Formation was formed in a subarid forest or grassland climate.
Cross bedded sandstone formations of the Jurassic, such as the Wingate, Navajo, and Nugget, represent fossilized sand dunes. These sandstones indicate an arid climate.
Casts of salt within the Alcova Limestone of southeastern Wyoming suggest intense evaporation in a very dry climate within the Triassic.
The deep red color of the rock and paleosols (A) along with the abundant calcareous and ironstone nodules or layers (B) in the Triassic of both the eastern and western United States suggest a semi-arid to arid climate.
