An artificial crater field that trained astronauts for lunar exploration.

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

Ancient pueblos built into the base of a natural canyon wall.

On the outskirts of a reborn ghost town, a decaying post office remembers the bad old days.

Ninety feet off the valley floor is an ancient dwelling put under protection of the U.S. government by Teddy Roosevelt.

Some of the tallest ancient American ruins continue to inspire awe and curiosity.

A geological mystery on Camelback Mountain.