Geology

The top of the holy mountain for the ancient Spartans looks like a pyramid—is it man-made or a natural phenomenon?

The world's largest mineral hot springs is home to a herd of bison, a free public bath house, beautiful mineral formations, and a terrifying swinging bridge.

An underground spring in a labyrinthine cave system, decorated with stalagmites and stalactites.

The original building of a mining school endowed by one of the barons of the Comstock Lode now houses a museum of earth science and mining history.

Crystal hunters can dig for their own stones at this DIY mine in Arkansas’ quartz belt.

One of Indiana's only natural sandstone arches is nestled between resort ruins and an old Boy Scouts camp.

This steaming, yellow-tinged landscape is filled with sulfur-encrusted volcanic vents.

Red ocher pictographs survive in this tufa rock shelter on the shore of an ancient lake.

One of the breathing caves of Australia's Nullarbor Plain.

These oddly shaped pink granite formations got their name after being mistaken for massive piles of hay.

This distinctive snowfield on the slopes of a Colorado fourteener has several legendary origin stories.

Nature has shaped this drainage tunnel into the digestive tract of a mighty beast.

This unique landscape is the only place in the world to dig for hourglass-selenite crystals.

One of the best places to dig—some say on the planet—for six different types of chalcedony.

Multiple waterfalls and several historic CCC buildings anchor this state park in Oregon's Willamette Valley.