Once disputed as the largest sundial in the world.

One of the most extensive and well-preserved collections of dinosaur footprints in North America.

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

This sinkhole in the Arizona desert is filled with carbonated, arsenic-rich water

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

Witnessing the might of this dessert-colored desert waterfall is a rare, powerful treat.

The eroded core of an ancient volcano is now accessible by a short hike.

This 24-acre park offers a place for meditation in the midst of Sedona's iconic red rocks.

A nature and cultural preserve named for its multitude of petroglyphs carved by the Northern Sinagua people.

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

Dyed by iron oxide over centuries, these sandstone rocks rise thousands of feet into the sky.

A volcanic tunnel illuminated by natural skylights offers a shaded respite from the desert sun.

The highest concentration of petroglyph sites in Gold Butte National Monument, plus an improbable early 20th-century dam.

See Hoover Dam and the bypass bridge from a perspective usually off-limits to the public, and float the upper part of the Black Canyon National Water Trail.

A mining town once rife with murderous disputes over its copious treasures now creates income as a popular spot for photo shoots.

A secret fresh water spring for animals and humans alike hidden along the most famous road in the United States.

Smooth basaltic rocks tell a tale of ancient glacial waterfalls.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

Get lost in this haunting fairytale art walk through a man-made eucalyptus grove.

A huge musical instrument played by the ocean.

An artsy hidden staircase leads to breathtaking views of San Francisco.

Part mural and part sculpture, this work of art sits in the middle of the Promenade, as if swimming in a river of asphalt towards the ocean.

Barely visible foundations remain where Stow Lake’s “observatory” once welcomed visitors.

San Francisco's urban bison herd has persisted in the face of extinction, development, and disease.