The Great Bend

The Great Bend. . A highland existed along the east side of South Dakota long before the Ice Age began two million years ago. Successive periods of glaciation deposited sediment across the highland and increased its elevation., The last glaciation began 35,000 years ago during the late Wisconsin Stage. By then the highland had become a barrier that divided the ice sheet into two south-flowing lobes: the James Lobe to the west and the Des Moines Lobe to the east. When the James Lobe reached the nearby southwest corner of the highland, it turned to flow east., In time the glacier began to recede. Meltwater flowing south down the Skunk Creek and Big Sioux River valleys was dammed by the James Lobe, causing it to flow east to Tuthill Park. There it was diverted several miles north before joining the Slip-Up and Split Rock creeks and then resuming its southerly flow. In this manner the Great Bend of the Big Sioux River was created by the James Lobe about 15,000 years ago., Glacial deposits overlay the flatiron-shaped highland that is now called the Coteau des Prairies.