The tectonic history of central Montana began with downwarp of the area accompanied by deposition of more than 13,000 feet of Precambrian-Cambrian-Ordovician sediments. Silurian, Lower Devonian, and Middle Devonian rocks are absent. During Late Devonian and Mississippian time, a thick marine sequence of carbonate and shale was deposited and during Pennsylvanian time, a thin nonmarine and marine sequence of clastics and carbonate was deposited. The area was then uplifted and truncated. Deposition resumed in Middle Jurassic and continued through Cretaceous terminating with uplift during the Laramide orogeny.