From mysterious gliding rocks in Death Valley to fossils of some of the most ancient life forms in Glacier, here are 11 lesser-known geologic wonders—including a few personal favorites from Bruce Heise of the Park Service’s Geologic Resources Inventory program.
1. No Water under the Bridge
Rainbow Bridge National Monument, Utah
Rainbow Bridge is one of the largest natural bridges in the world—so large that you could fit the dome of the U.S. Capitol underneath the bridge (not that you’d want to). Water played a crucial role in its formation. A stream first curved around a thin fin of soft sandstone before finally carving a hole in it. The erosional forces that created the bridge will eventually lead to its destruction, though water now rarely flows under Rainbow Bridge. The last time was 1999, when nearby Lake Powell overflowed.
2. Racing Rocks
Death Valley National Park, California
“Racing” may be a bit of an overstatement. Rocks weighing up to several hundred pounds have left plenty of puzzling tracks on the dry lakebed of “Racetrack Playa” in Death Valley, though nobody has seen the rocks actually move with their own eyes. The mystery was apparently solved in December 2013 when researchers using GPS devices, weather stations, and time-lapse cameras recorded the movement of more than 60 rocks—some gliding as fast as six meters a minute—as a thin layer of ice started to melt in the morning sun and light winds caused the rocks to move.
3. Puffin Pillows
Kenai Fjords National Park, Alaska
If you want to sleep like a rock, you’d better not sleep on one—unless it’s an outcrop of pillows and you’re a discerning bird. The colonies of horned puffins at Kenai Fjords have deemed the park’s pillow basalt perfectly adequate nesting habitat. The hardened lava, named for its pillow shape, forms at the bottom of the ocean when the lava cools quickly as it comes into contact with cold water. Tectonic forces then raised these rocks above the sea level, and they now form the cliffs that have turned into puffin habitat. The birds have now added their own layer to the outcrop. “They certainly stained it,” Heise said. “It’s not black basalt anymore.”
4. Cirque du Glacier
Rocky Mountain National Park, Colorado
The Fall River Cirque in Rocky Mountain is a bowl-shaped hollow created by glacial erosion. Unlike most glacial cirques, whose steep walls can only be accessed through climbing or strenuous hiking, this one requires no acrobatics and is accessible through one of the park system’s most scenic roads. “I don’t know of any other road off the top of my head that you can take to go all the way up a glacial valley and drive up the headwall of a cirque,” Heise said.
5. New Park, Old Rocks
Voyageurs National Park, Minnesota
Established in 1975, Voyageurs National Park is a relative rookie compared with the likes of Yellowstone or Yosemite, but the rocks at this northern Minnesota park predate those found anywhere else in the park system. Even the rocks at the bottom of the Grand Canyon are some 800 million years younger than Voyageurs’ oldest gneisses and schists, which formed as early as 2.85 billion years ago.
6. Life Begins at Glacier
Glacier National Park, Montana
Interested in how life on Earth started? Glacier’s fossils include remarkable examples of stromatolites, remnants of some of the Earth’s earliest forms of life. Sometimes resembling sliced cabbage, these fossilized layers of bacteria played a critical role in the development of life as they increased the atmosphere’s content of breathable oxygen. “You don’t see stromatolites just anywhere,” Heise said. “And they’re pretty important to the history of life itself.”
7. Fire Meets Water
Hawai’i Volcanoes National Park, Hawai’i
Witnessing a flow of molten lava is hard to top—except if that lava flows directly into the ocean, producing plumes of vapor in the process. Being able to view this rare spectacle involves a lot of luck. The good news is that Kilauea in Hawai’i Volcanoes National Park has been erupting continuously since 1983. The bad news is that these lava flows are unpredictable in their direction and intensity, so there is no guarantee one is headed for the ocean at any given time. You can check the current conditions here.
8. P.O. Box Wind Cave
Wind Cave National Park, South Dakota
Boxwork may not be the most grandiose of cave formations, but it’s one of the rarest and most mysterious. The elaborate pattern of paper-thin veins of calcite on the ceiling of Wind Cave was named for its resemblance to the cubby holes in the local town’s post office. The prevailing theory is that the calcite was more resistant than the surrounding rock material, which wore away through dissolution and erosion, leaving behind these striking shapes. What’s more, Wind Cave also features unusual formations such as cave popcorn and helictite bushes.
9. Inverted Hoodoos?
Bryce Canyon National Park, Utah
Bryce Canyon is famous for its hoodoos, columns of weathered rock ranging in size from the height of a human to that of a 10-story building. The harder rock on top protects the softer layer underneath from erosion to some degree (until that softer layer is eroded away and the hoodoo collapses). While most of the hoodoos at Bryce (and in the world) have younger rocks on top, the park includes a few examples of “inverted hoodoos” where the harder rock is actually older than the softer rock underneath. How did that happen? Tectonic forces pushed blocks of older rock over the younger layers before erosion took place. “When I had that pointed out to me, I was like ‘that’s the coolest thing I’ve ever seen,’” Heise said.
10. White Sand Factory
White Sands National Monument, New Mexico
The dunes at White Sands do seem otherworldly, but that doesn’t mean they’re from another planet. Actually, they form just a few miles away in the southwestern corner of the park. Crystallized gypsum forms below the surface of Lake Lucero, a smaller version of the larger Lake Otero that provided the bulk of the park’s white sand. Evaporation eventually exposes the crystals, which are then broken down and carried by wind before accumulating in the dunes. Lake Lucero is located in a restricted area of the park, but you can join a ranger-led tour of the lake from November to April.
11. Moving Mountains
Pinnacles National Park, California
Pinnacles’ namesake formations are jagged volcanic rocks that attract hikers and climbers alike. But learning where those rocks came from is what boggles the mind. Pinnacles used to be located about 200 miles south, near present-day Lancaster. The phenomenon responsible for Pinnacles’ current location is the same one that is to blame for the San Francisco earthquake of 1906. Tectonic forces along the San Andreas Fault moved Pinnacles’ rocks at a pace of a little more than half an inch per year over a period of 23 million years. The fault itself has shifted 4 miles to the east of the park.
About the author
Nicolas Brulliard Associate Editor
Nicolas is a journalist and former geologist who joined NPCA in November 2015. He writes and edits online content for NPCA and serves as associate editor of National Parks magazine.
- Bryce Canyon National Park
- Death Valley National Park
- Glacier National Park
- Hawai'i Volcanoes National Park
- Kenai Fjords National Park
- Pinnacles National Park
- Rainbow Bridge National Monument
- Rocky Mountain National Park
- Voyageurs National Park
- White Sands National Monument
- Wind Cave National Park