The U.S. is chock-full of breathtaking monuments, impressive parks, and archaeological landmarks. At such sites, structures, formations, and carvings have been etched into the American soil, providing a small glimpse into our country’s storied past. But what you may be surprised to hear is just how little we know about some of the most fascinating archaeological sites in the U.S.
Interested in learning more? Great. Check out some of the most mind-boggling mysteries we still know nothing about (and three bonus sites that are well worth the trip).
1. Casa Grande Ruins
Location: Coolidge, Arizona
The southwest is no stranger to ancient ruins and Native American history. But in Coolidge, Arizona, there’s one archaeological site — Casa Grande Ruins — whose purpose is relatively unknown. According to the National Park Service, “One of the largest prehistoric structures ever built in North America, its purpose remains a mystery.” And it’s remained a mystery for quite some time.
Built by the ancient Sonoran Desert people around 1350 C.E., Casa Grande, or “great house” is a complex structure. Furthermore, historians suspect that the structure served as a gathering place or a marker in a sizable canal system.
When the structure was abandoned around 1450 C.E., the ancient Sonoran Desert people left no written account. In 1694, European missionary Padre Eusebio Fancisco Kino visited the site, at which time he coined the name, Casa Grande, and began the first written accounts. Eventually, in 1892, the Casa Grande Ruins became the first prehistoric and cultural reserve in the U.S.
Next: Have you heard of Nazca Lines before?
2. The Blythe Intaglios
Location: Blythe, California
Often referred to as America’s Nazca Lines, the Blythe Intaglios lie just north of Blythe, California in the Colorado Desert. The series of geoglyphs features six figures — drawings of humans, animals, objects, and geometric shapes — located on two mesas. And the real mystery here is not only who created these figures, but when.
The site was first discovered in 1931, and then in 1952, National Geographic published a series of aerial photos. Most historians believe that Native Americans who lived along the Colorado River are behind the Blythe Intaglios, but not much else is known. Additionally, according to the Native Mohave and Quechan tribes, the human figures represent Mastamho, the Creator of Earth and all life, and the animal figures represent Hatakulya, a mountain lion or person imperative to the Creation story.
Next: These rock carvings are super impressive.
3. Hemet Maze Stone
Location: Hemet, California
While there are a number of similar patterns on rocks in the surrounding areas, the Hemet Maze Stone is the most notable, and has left scientists, historians, and archaeologists alike completely baffled since it was discovered in 1914.
The main attraction at this archaeological site? A boulder with a highly-detailed drawing of a maze, all within a three and a half foot square that dates back to 2000 BC. Geometry prodigy? Perhaps, but we still have no idea who or why.
Next: Simple rock walls have left experts scratching their heads.
4. Berkeley Mystery Walls
Location: San Francisco, California
A series of low-walled rock piles, the Berkeley Mystery Walls run across California’s Bay Area. Although their exact purpose is unknown, there are some theories about the origins of how — and why — these walls came to be.
Research supports that the walls were created during the early American era. Furthermore, according to The Mercury News, “The walls were used mainly to clear land of scattered rocks to facilitate the movement of grazing livestock, such as cattle, and, at times, to guide the movement of the animals or to corral them.” Yet, the exact origins remain unknown.
Next: These place features six prehistoric villages.
Location: Colorado and Utah (between Cortez, Colorado and Blanding, Utah)
A unit of the National Park System since 1923, Hovenweep was once home to over 2,500 people. Undoubtedly the most impressive element of this archaeological site is its structures, which date back to about A.D. 1200. In fact, there must have been some design prodigies in the group that built Hovenweep’s six prehistoric villages.
According to NPS, visitors can “explore a variety of structures, including multistory towers perched on canyon rims and balanced on boulders.” More specifically, the architects responsible for these structures were the ancestral Puebloans. The buildings may have served any number of functions, from observatories to defensive structures to storage facilities. It’s anybody’s best guess.
Next: This southern spot was only discovered in the late 90s.
6. Miami Circle
Location: Miami, Florida
As the name suggests, this archaeological site contains a number of large holes forming a perfect circle. The interesting part about it, though, is what was discovered inside the circle. In 1998, excavators found a wide range of artifacts including human teeth and ancient tools. Furthermore, Atlas Obscura reported, “To date, Miami Circle is the only known evidence in the United States of a prehistoric structure built into bedrock.”
With a number of contradictory theories, the Miami Circle is a mind-boggling mystery to most.
Next: Let’s head up north for this next one.
7. Dighton Rock
Location: Berkeley, Massachusetts
Dighton Rock is a 40-ton boulder that made its way to Massachusetts during the last ice age. Covered in petroglyphs, the rock has left experts scratching their heads about the meaning and creators behind the inscriptions. In fact, the carvings have inspired over 1,000 books and articles. There are over 35 various hypotheses about the origin of the inscriptions on Dighton Rock.
Next: This place is kind of like Stonehenge, just not nearly as impressive (or famous).
8. Mystery Hill
Location: North Salem, New Hampshire
Sometimes referred to as America’s Stonehenge, Mystery Hill is made up of complex rock formations. The site may date back to the early 17th century, but still, the exact date of origin is unknown. And when it comes to who exactly built it, the theories are vast.
So, who could have built this? Historians have suggested Irish Culdee monks, an individual names Jonathan Pattee, Goidelic Celtics, and Native Americans. While the creator(s) may be a mystery, there’s a commonly held belief regarding the purpose of Mystery Hill. Most likely, the structure existed as a religious or ceremonial center.
Next: Researchers are still quite confused by this one.
9. Chaco Canyon
Location: New Mexico (between Albuquerqie and Farmington)
Chaco Canyon is certainly a sight worth seeing. It features impressive Pueblo buildings which have stood the test of time. In fact, these structures prove that the ancient Pueblos mastered their craft of organization and engineering like no other group in the American Southwest. And while we know that the Pueblo people inhabited this space between 850 and 1250 A.D., the carefully constructed design leaves us in awe.
After recognizing the need to protect a much more expansive area of land, congress passed an important law. In 1980, congress changed Chaco Canyon’s status from a national monument to a national historical park. With all of its architectural feats and long-lasting structures, NPS says, “Chaco is also an enduring enigma for researchers,” and we may never be able to fully grasp the operation that happened centuries ago.
Next: A Cherokee legend is behind this one.
10. Judaculla Rock
Location: Sylva, North Carolina
Not even experts have been able to decipher exactly what this petroglyph-clad boulder is all about. But what archaeologists do know is that is could be about 2,000 to 3,000 years old.
While we’re not sure who put the carvings there in the first place, the Cherokee Indians consider Judaculla Rock to be an ancient and significant site. In fact, Cherokee legend has it that Judaculla — a giant who roamed the mountains and controlled the weather — is responsible for the rock’s markings.
Next: This one is best seen from the sky.
11. The Great Serpent Mound
Location: Hillsboro, Ohio
There’s much debate around the Great Serpent Mound in Ohio, and researchers have come up with plenty of contradicting theories regarding when, why, and how the mound came to be. Located in southern Ohio, the snake-shaped mound is 1,330 feet long and three feet tall.
As for who built it? The Adena culture is a good guess, seeing as they’d built structures and burial grounds near the Great Serpent Mound. But the presence of charcoal discovered within the mound suggests that the Fort Ancient people of the Ohio Valley (1000 CE to 1550 CE) could be responsible.
Next: This has long been a sacred Native American display.
12. Bighorn Medicine Wheel
Location: Lovell, Wyoming
Compared to most other monuments on the list, a fair amount is known about the Bighorn Medicine Wheel. While there are numerous medicine wheels — wheel-like arrangements made using stones — in North America, this one is perhaps the most notable thanks to its size.
Stretching a whopping 75 feet in diameter, Bighorn Medicine Wheel is a sacred monument to many Native American tribes across the Great Plains. The site was likely used for astronomy, but the original creator of this medicine wheel remains to be seen.
Next: The remaining three spots aren’t unexplained, but they’re definitely worth the visit.
13. Mesa Verde
Location: Montezuma County, Colorado
Often described as the most impressive archaeological site in the country, Mesa Verde is a stunning display. Once home to the Ancestral Pueblo people from AD 600 to 1300, Mesa Verde is a national park and World Heritage Site chock-full of incredible cliff dwellings built right into a rocky mountainside.
Next: Another mesa makes an appearance on the list.
14. Cedar Mesa/Grand Gulch Plateau
Location: San Juan county, Utah
This destination is not for the faint of heart, or heat. Cedar Mesa and Grand Gulch Plateau is situated in a hard-to-get-to desert environment. Once home to Ancient Puebloans, visitors can find rock structures, broken pottery, and rock art images throughout the area.
Next: These stunning cliff dwellings will leave you inspired.
15. Montezuma Castle
Location: Camp Verde, Arizona
Located just 50 miles south of Flagstaff, Arizona, Montezuma Castle is home to some of the most stunning cliff dwellings in the U.S. The ruins’s main attraction is a five story, 20 room dwelling, which was more or less a high-rise apartment building for the prehistoric Sinagua Indians over 600 years ago.
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