The USGS Central Region Energy Team assesses oil and gas resources of the United States. The onshore and State water areas of the United States comprise 71 provinces. Within these provinces, Total Petroleum Systems are defined and Assessment Units are defined and assessed. Each of these provinces is defined geologically, and most province boundaries are defined by major geologic changes.
The Powder River Basin Province is located in northeast Wyoming and southeast Montana with some assessment units extending beyond the existing province boundary into small areas of southwest South Dakota and northwest Nebraska. The province encompasses all or parts of Big Horn, Campbell, Carter, Converse, Crook, Custer, Fall River, Fallon, Johnson, Natrona, Niobrara, Powder River, Rosebud, Sheridan, Sioux, Treasure, Weston, and Yellowstone counties in the states listed above. Main population centers (greater than 15,000 residents) within the study area are Casper and Gillette, Wyoming. Interstate 90 generally traverses the province from east to west while I-25 runs north to south. The province boundary was drawn to include the geologic structures generally considered to be in or bounding the Powder River Basin along with some political boundaries as guides.