The Ten Most Spectacular Geologic Sites

Smithsonian picks the top natural wonders in the continental United States

Meteor Crater in Arizona is 4,000 feet wide and almost 600 feet deep. (iStockphoto)

Certain travel destinations remind you that you live on a planet—an old, weathered, tectonic-plate-shifting planet. The Earth has been smothered by glaciers, eroded by wind and water, splattered with lava and slammed by debris from outer space. Yet these geologic forces have left behind some of the most fascinating must-see sites in the continental United States.

10. Lava Beds National Monument, California

Volcanic rock is vicious stuff: black, jagged, crumbly and boot-shredding. But if you look at it right, you can sense the power of the volcano that spewed it out. The Medicine Lake volcano at the northern border of California has been erupting for half a million years. (Its last gasp was 900 years ago; the next one? Who knows.) The volcano has produced some awesome classic geologic features that are easily accessible at Lava Beds National Monument.

You can see tuff (compacted ash), long flows of pahoehoe (ropy, rounded lava) and aa (the pointy rock named for the exclamations one makes when trying to walk across it). Cinder cones surround vents where lava erupted in short, gassy blasts; spatter cones were formed by thicker, heavier lava.

But the highlight of the national monument is the lava tubes. When lava flows in channels, the exterior can cool and solidify while the interior is still hot and molten. If the lava inside flushes through, it leaves behind a warren of surreal caves that are just the right size for spelunking. The park has the longest lava tubes in the continental United States; bring a flashlight to explore them. Some are deep and dark enough that they have ice year-round.

9. The Ice Age Flood Trail, Washington, Oregon and Idaho

During the last ice age, about 18,000 to 12,000 years ago, an immense lake covered the western edge of Montana. The lake water was trapped by a glacier along the Idaho panhandle that acted as a dam. When the dam melted, the entire lake—as much water as in Lake Ontario and Lake Erie combined—surged across Idaho, Oregon and Washington to the sea. It drained in about two days.

This epic flush may sound like the flash flood of all flash floods. But the whole process happened repeatedly during the last ice age and during previous ice ages as well.

These massive floods gouged out basins all along the Columbia River, deposited 200-ton boulders throughout the area and scoured the territory now known as the Scablands.

A bill to create an Ice Age National Geologic Trail (more of a driving route than a hiking trail) passed Congress this year and would establish information centers at some of the more dramatic flood sites.


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