Sandstones of the Lance and Fort Union Formations

The Fort Union and Lance formations are widespread terrestrial sediments exposed in Montana, North Dakota, South Dakota, Wyoming, and Canada. Their stratigraphic position, especially that of the Lance, has long been in doubt, and has provoked much controversy among geologists.

The Fort Union Formation of Montana and Adjacent Areas

The Fort Union formation is one of the most import­ant and best known geologic formations of the northern Great Plains, and is found lying almost horizontal at the surface over large areas in this region.