Looking at the rocks, sand and sidewalks beneath our feet, you might get the impression that the earth is permanently fixed in place, immobile and unchanging. But in fact the ground is changing all the time, from earthquakes and volcanoes reshaping regional geology to the continental drift that has brought our continents together and apart again and again throughout geologic history.

The United States has seen its fair share of geologic upheaval – mountain ranges in the east and west, earthquakes on the West Coast, active volcanoes like Mount St. Helens, and even the quietly rumbling Yellowstone supervolcano.

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These ongoing geologic processes have created some of the country's most breathtaking natural rock sculptures, from the jagged Tufa Towers in Mono Lake, Calif. to the ancient volcanic eruption of Shiprock in New Mexico.

In the slideshow above, explore some of the strangest and most amazing rock formations in the country. Which is your favorite, and which park would you most like to visit to see these wonders?