Buffalo Ridge, on the Bemis moraine about one kilometer north of Lake Benton, is the second highest point in southwestern Minnesota and marks a drainage divide between the Mississippi and Missouri River watersheds, with Lake Benton draining east to the Mississippi River and the Flandreau River draining west to the Missouri River. The ridge is a moraine, a mass of silt, sand, gravel, and boulders left at the edge of a glacier, and the Bemis moraine formed on the western side of an ice lobe that originated in Canada and extended south into Iowa 14,000 years ago. At Lake Benton, a break in the moraine about one to two kilometers wide is matched by similar but less spectacular breaks at Lake Hendricks and Lake Shaokatan to the north. In each case, a straight wide channel now occupied by a long lake lies on the east side of the break; these tunnel valleys were cut by forceful water flowing beneath the melting glacier. On the west side of the moraine, beyond the former ice margin, rivers follow sinuous channels of varying width, meandering stream valleys carved by glacial meltwater flowing out from the tunnel valleys. The contrast between the valleys on the two sides of the moraine reflects pressure: beneath the ice, heavily pressurized water could even flow uphill, so the floor of the tunnel valley slopes upward toward the moraine, while after emerging from under the glacier, released from that pressure, the water was free to meander.