What on Earth Made This?

1. Delicate Arch
Arches National Park, Utah
A double-decker bus could easily fit through the span of this giant sandstone arch. It is Utah's state symbol, celebrated on license plates and tourist tchotchke. What made it?

1. viscous lava
2. wind and water erosion
3. lightning strikes

2. The Devil's Postpile
East Sierra Mountains, California
South of Yosemite National Park, an astounding assemblage of tightly packed rock columns stretches 60 feet skyward. Over half of these rocky posts have six sides, like the chambers of a honeycomb. What made the postpile?

1. a moving glacier
2. a prolonged earthquake
3. slow-cooling lava

3. Barringer Crater
near Winslow, Arizona
In the middle of a barren plain of Arizona desert exists a depression so big it could easily cup a large suburban shopping mall. At its rim lie jumbled sandstone boulders the size of small houses. What made the crater?

1. an explosion of volcanic steam
2. a meteorite
3. erosion by a former lake

4. Archeopteryx
Solnhofen, Germany
This fossil from the Jurassic shows, in fine detail, the trace of a small dinosaur with feathers. It revolutionized our understanding of how birds evolved. What made it?

1. arid conditions and calcification
2. acids in the dinosaur's skin and feathers
3. the environment of an ancient salty lagoon

5. Potholes
Channeled Scabland, Washington State
Rather than drive over these giant potholes, you could drive a motorcade of cars inside one. Hundreds of potholes—some over 100 feet in diameter and nearly as deep—mark the landscape. What made them?

1. underwater vortexes
2. a surging, acidic river
3. explosions of volcanic steam

6. Pumpkin Patch
Colorado Desert, California
In dim light, you might mistake these rocks for vegetables. They look like pumpkins in size, shape, and even distribution. But there are no vines in sight. What made them?

1. retreating glaciers
2. minerals that precipitated around objects
3. artists paying homage to California produce

7. Karst Pillars
Guangxi Province, China
Thousands of knobby limestone towers—some as tall as 1,500 feet—make this region of southern China a mecca for sightseers and intrepid rock climbers. What made them?

1. the same forces that carve caves
2. monsoons
3. volcanic extrusions

8. Old Man of the Mountain
Franconia Notch, New Hampshire
He was the celebrated guardian of the White Mountains. From forehead to chin, his imposing granite profile measured 40 feet. But on May 3, 2003, he met his demise in a calamitous, naturally caused rockfall. What made him?

1. sculptors practicing for Mt. Rushmore
2. an earthquake
3. glaciers and ice wedging