A turkey vulture flies over Lewis and Clark Caverns State Park, near Whitehall, Mont.

The famed Corps of Discovery never found these natural wonders, though. They passed them on their way through the mountains, along the Jefferson River.

Many of the limestone formations inside the caverns have been named clever things by park service guides. You're looking at a stalagmite called "Old Faithful" and in the lower right corner, a broken column dubbed "the Fallen Idol" that is estimated to weigh eight tons.