One of the fiercest battles of the U.S.-Dakota War of 1862, the fight at Birch Coulee erupted when Dakota forces ambushed an encampment of Minnesota state troops and civilians on the morning of September 2, 1862. Dakota forces laid siege to the camp for thirty-six hours before relief arrived from Fort Ridgely. Although the camp was not overrun, twenty men and ninety horses were killed on the U.S. side, while Dakota losses are unknown.