Dakota Sandstone

The Dakota Sandstone, formally the Dakota Formation, is a sedimentary geologic unit of the Midwestern and western United States and adjoining Canada, extending from British Columbia and Alberta south through Montana and Wisconsin and further south through Colorado and Kansas to Utah and Arizona, dating to the mid-Cretaceous Albian to Cenomanian ages, roughly 100 to 95 million years ago. It consists of sandstone, mudstone, clay and shale deposited as the Western Interior Seaway opened, with the sandstones commonly colored red, gray, yellow or white depending on iron oxide or calcite cement, and secondary marine shale, lignite and coal; it forms the important Dakota Aquifers of the Great Plains and Southwest and hosts economically valuable lignite, coal and uranium. The formation preserves dinosaur footprints and fossil leaves of early deciduous trees, along with dinosaur body fossils including the ankylosaur Silvisaurus condrayi.