Born of Volcanos

Born of Volcanos. . Thirty-seven million years ago, the ancient crystalline core of the Black Hills had already been exposed by erosion. The long blue profile of those mountains, visible to the west, looked much as it does now. , About that time, streams flowing from the west began to deposit sediments in this area. Most of the sediment was wind blown volcanic ash which had settled into the watershed which fed the streams. Occasionally the rivers brought gravel and stream-worn rocks from the Black Hills themselves. The ash weathered into clay, and turned into rock. , Erosion did not begin to gully the Badlands layers and foretell the present landscape until quite recently, perhaps only half a million years ago.