The Upper Yellowstone Pompeys Pillar Watershed (HUC 10070007) covers an area of approximately 4,042 square miles in south-central Montana. The area is predominantly grassland and shrubland, with some forested areas. The hydrology of the watershed is dominated by the Yellowstone River, which flows through the area. The snowpack in the area is generally moderate, with an average snowfall of around 50 inches per year. The surface water in the watershed is primarily supplied by the Yellowstone River and its tributaries. There are several small reservoirs in the area, but they do not significantly contribute to the water supply. The climate in the area is characterized by cold winters and warm summers, with an average annual precipitation of around 15 inches. One interesting climatic fact is that the area experiences occasional droughts, which can have significant impacts on the local agriculture and wildlife.