The Greenhorn unit name is recognized in the Great Plains Region from Minnesota and Iowa to New Mexico to Montana and the Dakotas.

[3] In Kansas, the Greenhorn Formation is divided into the (lowest) Lincoln Limestone, Hartland Shale, Jetmore Chalk, and (highest) Pfeifer shale members, each noted by changes in chalkiness and limestone rhythmite patterns.

The combination of the toughness of the Fencepost limestone with the softness of the chalk and shale above and below as resulted in the formation of the main range of the Smoky Hills north and west of Salina.

[8] The oceanic iron (Fe) and volcanic sulfur (S) that precipitated with the volcanic ash into the calcareous mud (CaCO3) formed pyrite (FeS2), which later altered to selenite (CaSO4·2H2O), siderite (FeCO3), and limonite (FeO(OH)·nH2O),[9] leading to the yellow to orange staining.

The formation is recognized for its sequence of index fossils, including oysters, Ammonoidea, Belemnitida, and Inoceramidae.