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 San Juan Basin Province is located in South Western Colorado and North Western New Mexico, encompassing all or parts of Montezuma, La Plata, and Archuletta Counties in Colorado and all or parts of San Juan, Rio Arriba, Sandoval, Mckinley, Bernalillo, and Cibola Counties in New Mexico. The main population centers within the study area are Durango Colo.; and Farmington, New Mexico. The San Juan River and Animas River and their tributaries drain the area. The province boundary was drawn to include the geologic structures generally considered to be in or bounding the San Juan Basin