The Lower Mississippian Mission Canyon Formation and stratigraphic equivalents in Montana and Idaho were deposited on a progradational carbonate ramp that developed on the foreland side of the Antler foredeep. Shallow subtidal and peritidal lithofacies were deposited in ramp-interior settings across most of Montana. The ramp to basin transition in westernmost Montana was a relatively narrow belt of stacked skeletal grainstone banks. Farther west, skeletal grainstone banks prograded over and interfingered with outer ramp/slope cherty limestones. In east-central Idaho, coeval lower slope and basinal strata consisted of silty to argillaceous, spicular limestones, spiculites, and spicular calcareous siltstones/fine-grained sandstones.
Carbonate Sequence Stratigraphy: Recent Advances and Applications, American Association of Petroleum Geologists Memoir, Vol. 57, 1994, 327-352.