From Smithsonian Magazine
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. Smithsonian picks the top natural wonders in the continental United States.
Among them are Lava Beds National Monument, California; The Ice Age Flood Trail, Washington, Oregon and Idaho; Mammoth Cave National Park, Kentucky; and San Andreas Fault at the Carrizo Plain, California.
