Lake Circle was a glacial lake in eastern Montana during the late Pleistocene, formed when meltwater from the retreating Laurentide Ice Sheet pooled along the Redwater River in a basin enclosed by a preglacial valley and the ice margin. Its remnants are linked to a broad abandoned valley southwest of Nickwall that extends north from Redwater Creek to the Missouri River. The valley’s wide, poorly drained floor, flat uplands, and contrast with nearby V-shaped coulees show sedimentation from the lake rather than normal stream erosion. The lake belongs to the late Wisconsin glacial episode, when the Havre lobe dammed the ancestral Missouri River.