Bentonite, originally known as “mineral soap” or “soap clay,” was named “bentonite” in 1898 by Wilbur C. Knight for deposits in the Benton Shale near Rock River, Wyoming. The Benton Shale included Upper and Lower Cretaceous units lying between the Niobrara and Cloverly formations and their equivalents. Currently named equivalent stratigraphic units in Wyoming include the Frontier Formation, Carlile Shale, Greenhorn Formation, Belle Fourche Shale, Mowry Shale, Aspen Shale, Muddy Sandstone, Newcastle Sandstone, Thermopolis Shale, Skull Creek Shale, and Bear River Formation. The best Wyoming bentonite is found primarily in the Upper Cretaceous Mowry Shale.

According to the Wyoming Mining Association, bentonite deposits in Wyoming comprise as much as 70 percent of the world's known supply, making the state the nation's leader in bentonite production. Surface mining to depths no greater than about 50 feet accounts for all bentonite production. Bentonite is mined in Wyoming from numerous pits in various areas of the state. Major producing districts are the Northern Black Hills (Colony) District, Southern Black Hills (Clay Spur) District, Kaycee District west of Kaycee, and Eastern Big Horn Basin. Bentonite from pits in these areas is blended, ground, dried, and processed into various products at 15 active mills in Wyoming.