Near Highway 200, glaciers once advanced out of the Mission and Swan ranges and the mountains in the Bob Marshall-Scapegoat wildernesses, forming an ice cap connected to the Cordilleran Ice Sheet that nearly filled valleys to the peaks from Salmon Lake to the Flathead Valley. Over about 300,000 years during the Bull Lake and Pinedale ice ages, glaciers repeatedly shaped this part of Montana. During the Bull Lake Ice Age about 140,000 years ago, glaciers flowed farther south in valleys south of Ovando and Helmville. Between 60,000 and 15,000 years ago the ice cap formed again, and southward-spreading glaciers carried gravel and sand into the Ovando area. As the glaciers melted, they left moraines of rock and soil debris, hollows that filled with water and remain today as wetlands, shallow ponds, and small lakes, kettles north along Highway 83 formed by melting buried ice, and broad outwash plains to the north and east created by powerful meltwater streams. Those valleys are now agricultural land along the Clearwater and Blackfoot rivers.