West Saint Paul Antiques

During the epochs that followed, the land continued to change. Deposition from the mountains in the west continued throughout much of the Eocene, Oligocene, and Miocene epochs. Then as the Pliocene Epoch began, erosion dominated and the layers began to be stripped away. Rivers meandered through broad, shallow valleys across the western Dakotas and eastern Montana plains. Although the rivers changed their courses many times, when the Pliocene Epoch came to a close about two million years ago, one of these rivers existed in almost the same position as the modern Little Missouri River. This river flowed northward to merge first with the ancestral Yellowstone River near Williston, North Dakota, and then merged with the Missouri River, continuing northeastward through Saskatchewan and Manitoba to Hudson Bay.

In the Pleistocene Epoch, the time period of numerous Ice Ages, which began about two million years ago, great continental ice sheets advanced southward from present-day Canada and reached as far as the upper North Unit boundary in the park. The ice blocked the flow of the north-flowing rivers, forcing them to create new courses eastward and southward, causing them to empty into the Mississippi River instead of Hudson Bay. By the time the ice retreated, the northern portions of both the Little Missouri and Missouri rivers were entrenched in their new channels. The Little Missouri’s new course to the north followed a steeper course, causing the whole river to flow faster and begin cutting deeply into the land. Slicing easily through the soft sedimentary rocks, the river and its tributaries carved the fantastically broken topography that is today’s badlands.