The Upper Missouri Dearborn Watershed (HUC 10030102) covers approximately 3,157 square miles in western Montana. It is primarily a mountainous region with elevations ranging from 3,000 to over 9,000 feet. The watershed is characterized by its large snowpack, which typically accumulates between November and April, and provides a significant portion of the surface water for the region's rivers and streams. The area is also home to several reservoirs, which store water for irrigation, hydroelectric power generation, and recreation. The climate in the watershed is characterized by cold winters and warm summers, with average annual precipitation of around 25 inches. In recent years, the region has experienced warmer temperatures and less snow accumulation, which may have implications for water availability and ecosystem health. The Upper Missouri Dearborn Watershed is an important resource for the region, providing water for agriculture, industry, and recreation.