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.
