Glacial Lake Agassiz and the Red River Valley

The Red River Basin has its origins in Glacial Lake Agassiz. About 14,000 years ago during the Ice Age, the continental glacier covered the Basin. As glacial ice retreated northward, Glacial Lake Agassiz formed about 12,000 years ago. The lake drained to the south through what is now the Minnesota River valley, to the west through northern Saskatchewan to Alaska, and to the east to the Great Lakes.

Mahnomen County is on the far eastern edge of what was Glacial Lake Agassiz.