Around half a million years ago, these magnificent columnar basalt cliffs were formed from cooling lava.

A 6-mile-long lake created by an apocalyptic seismic event and the deadly chain reaction that ensued.

The only natural lake in the world that drains into both the Atlantic and Pacific Oceans.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

One of nature's most well-scheduled phenomenons resides in Wyoming's Yellowstone National Park.

Tucked away on a scenic trail, a modest memorial honors one of the greatest writers of our time.

Home to the deepest rift anywhere on Earth.

These falls, sometimes called the "Niagara of the West," still put on a good show at the right time of year.

Quite simply the largest tree in the world (by volume).

A remote desert lookout offers unparalleled views of the California badlands for those who brave the trek.

This oasis-like spring in the Sonoran Desert is home to unique, endangered species.

A strenuous, unofficial trail leads to spectacular views in one of America's most remote national monuments.

This 40-room dwelling tucked within a cliff was built by the basin's prehistoric residents.

After a short-lived attempt to bring America in line with the rest of the world, this road was left in metric.

During World War II this was the site of an "honor camp" used as a prison for draft dodgers, Native American conscientious objectors, and Japanese-Americans—including a man who brought his case against the camp to the Supreme Court.

Limestone caves with spectacular showcase chambers.

Hike the unusual hoodoos and rock formations that form this little-known natural wonder.

The former home of the army detachment that captured Geronimo.

The largest copper mine in Arizona, this enormous open pit emerges from the hills like an alien landscape.

This Old West prison built into the side of a cliff was said to be inescapable.

See massive fossils that are over 200 million years old in northeastern Arizona.

The hike through a narrow river flanked by the 2,000-foot-tall walls of Zion Canyon is one of the best in the world.

Erosion and various mineral deposits give this striking canyon its distinct color and soft appearance.

This once-booming Gold Rush town is now home to a herd of feral donkeys.