The Turtle and the Serpent

Stages in the Development of Turtle Mountain

1. 30,000 BC

Map: maximum extent of the Wisconsin ice sheet.

Maximum extent of the Wisconsin glacial period. The glacier, flowing generally from northeast to southwest, has penetrated the Missouri Plateau (brown) in places, leaving isolated limestone buttes.

2. 12,000-6,000 BC

Map: glacial retreat.

As the glacial front retreats towards the northeast, the troughs it gouged out fill with floodwater. A series of lake levels fill and empty in turn as the glacier and the floodwaters diminish.

3. 10,000 BC

Map: maximum extent of glacial Lake Agassiz.

A snapshot of the land as it might have been about 10,000 BC when all of the Turtle Mountain region was free of ice and the Spirit Sands Delta had been formed.

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