Driving into Pipstone, you'll see some large rocks just off the entrance road. These are the Three Maidens, sacred to the native people who collected the pipestone, and they traditionally left offerings here before quarrying (they still do). Geologically, they are glacial erratics of granite which were picked up somewhere to the north by the glaciers and dumped here when they melted atop the very different bedrock of Sioux Quartzite.
According to the Pipestone website:
Historically, there were 79 petroglyphs on 35 slabs of rock placed around the three maidens. The carvings depicted various forms such as people, animals, bird tracks, and more. The petroglyphs were removed in 1888 or 1889 after some had been defaced. The stones changed locations many times before some of them were returned to Pipestone National Monument in the mid-1900s. Seventeen of the petroglyphs formerly placed at the Three Maidens are now on display in the Visitor Center.
Here's a picture of one petroglyph on a slab on display at the visitor's center. Oddly enough, it looks like Anasazi shaman-type images I've seen in Utah.
Here's a partial image from a park sign showing the mining of the pipestone. C represents the prairie soil which is of varying thickness (looked to be over a foot thick where I saw it). B represents the hard Sioux Quartzite which has to be removed to access A, the layer of catlinite mined for pipe stones. At Pipestone, the layer of catlinite is slightly dipping to the east so one must continually quarry deeper and deeper to obtain it.
Geologically, catlinite is a type of argillite - a metamorphosed mudstone. In this area, 1.7 billion years ago, quartz sands accumulated with occasional influxes of clay mud. Metamorphism altered the sands into the Sioux Quartzite and mud layers into the catlinite. The red color in catlinite comes from iron oxides and its fine-grained texture and softness (about as hard as your fingernail) allows it to be easily carved. Native Americans quickly figured out it could be shaped into pipe bowls and it became highly prized with Indians coming from all over the Midwest to mine and trade it. Native Americans are still allowed to mine at Pipestone even though it's a national monument.
There were two guys carving the pipestone in the Visitor's Center and it was interesting to talk to them. The basic technique is simple - the pipestone blanks can be cut with a hacksaw into a rough shape and then rasped down. Detail work is done with smaller files (ancient people used pieces of flint, deer antler, bone, etc.). Then it's sanded and beeswax rubbed into it for a glossy finish.
Catlinite was named for George Catlin (1796-1892), the famed artist who specialized in Native American portraits. Catlin visited Pipestone in 1835 and painted the following scene. Note the Three Maidens off to the right, the waterfall and cliff line, and the trenching for Pipestone.
It's a bit more overgrown now. Here's a picture from the cliff face.
More of the cliff face - note the old Indian profile (not intentionally carved).
Here's a modern quarry the Native Americans are using to access the pipestone (it needs to be pumped out of water).
Here's a quarry face the park service prettied up for tourists to visit. See the thin layer at the base of the cliff face? That's the pipestone.
Here's a closeup of the pipestone layer. It may be hard to tell, but it's significantly different looking (and softer) than the overlying Sioux Quartzite.
So, after leaving Pipestone, it was a long hard drive through South Dakota to Wall. On the way, we stopped at Mitchell, home of the world famous corn palace!
Those murals on the outside of the corn palace (and also inside)... They're made of ears of corn. Truly one of the wonders of the Western world.
We finally reached Wall, SD around dinnertime. For those who've never driven I-90 through South Dakota, Wall is the home of Wall Drug. You can't not stop at Wall Drug when passing through South Dakota (especially with kids). Free ice water, 5 cent coffee, and millions of trinkets you can buy in dozens of stores (they actually have a very good Western book store too). Also statues and animatronic T-rex dinosaurs and such to amuse the kids. I've taken to hugging the bunny every time we stop.
Sunday night was Motel 6 in Wall. Good thing too, the car thermometer said it was 115 F outside at one point (it was damn hot and I wasn't about to set up a tent in the Badlands!).