10 of the United States' Most Intriguing Archaeological Mysteries

There are quite a few places where early Americans left their marks, but did not leave us any explanations. European explorers had never seen anything like them, and local people said they’d always been there for reasons lost to time. Many of these mysteries are symbols or possibly language carved in rocks. One huge design in California wasn’t even discovered until a plane flew over in the 1930s! And then there’s the Miami Circle.

A recent discovery, the Miami Circle was only unearthed in 1998 when a Florida developer knocked down a 1950s apartment complex, revealing a circular pattern of holes in the limestone bedrock. Further excavation turned up tools similar to those used by the once-local Tequesta people, and radio-carbon testing suggests the site is nearly 3,000 years old.
The State of Florida now owns the plot, which still sits at the water's edge beside a series of high-rises, to protect it from developers. Archaeologists believe the holes are actually signs of a bit of prehistoric development: post-holes for some kind of permanent shelter.

Read about nine more of these America mysteries at Atlas Obscura.