Sioux Falls

It's so easy to generalize the Great Plains or the Midwest into monolithic landscapes - horizontal, two-dimensional landscapes. And there is some validity to that, but what's neat to me is that this is exactly what makes their hills and their valleys and their forests and their waterfalls so interesting.

Geologically, it's also easy for me to forget that bedrock, sometimes very old bedrock, can be exposed in these areas - not just covered in a blanket of glacial silt or tilled corn fields.

Driving from Seattle to Boston on I-90, you might never stop to think that there really are falls in Sioux Falls (and you would certainly never see them), but that's why it is important to get off the highway now and then.

During the last ice age, the Big Sioux River got rerouted by the glaciers and then it eroded down to bedrock - in this case the incredibly resistant Sioux Quartzite - and the modern falls were formed. Just like along the fall line of the Atlantic Seaboard, waterfalls were navigation barriers and power sources, so cities were built.

The Sioux Quartzite is roughly two billion years old (half the age of the earth and long before any kind of life we would recognize). And two billion year-old ripples are still preserved on its eroded surface.