The underlying bedrock of this region is composed primarily of Pierre shale in the northern portion of the Prairie Coteau and* Sioux Quartzite at the southeastern edge of the Prairie Coteau. Exposed Pierre shale, with its coal-like appearance, can be seen on the eastern escarpment on South Dakota state highway 10 west of Sisseton, South Dakota. Sioux Quartzite is exposed in many places from the cutting action of water over time and displays beautiful rugged formations, one of which creates a waterfall from which the city of Sioux Falls, South Dakota derived its name.