10 U.S. Landmarks That Have Left Experts Stumped – And 10 Whose Mysteries Have Now Been Unraveled

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The United States has many stunning historic sites – no small number of which date from millennia before European settlement of the land. Careful study of some of these archeological gems has revealed their secrets, but other sites have baffled researchers with enduring and intriguing mysteries. Read on to find out about some of these outstanding sites – from the explained to the enigmatic.

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20. Casa Grande Ruins

Just north of the modern city of Coolidge, Arizona, there’s an ancient site known as the Casa Grande Ruins National Monument. The buildings date back to sometime around 1350, and archeological evidence shows that the ancestral Sonoran Desert people built these structures. Apparently, they lived in southern Arizona for around 1,000 years until about 1450 and built a sophisticated network of irrigation canals in the region that supported their agriculture.

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The centerpiece of the site is the Casa Grande – or Grand House. Italian Jesuit priest Padre Eusebio Francisco Kino gave it that former name when he happened across it in 1694. The Grand House is built from caliche, which is a naturally occurring aggregate stone. And it’s certainly stood the test of time – still standing some 700 years after it was erected. The site is surrounded by low walls and includes the remains of various other structures. But what was the purpose of these structures? That remains an unsolved puzzle to this day.

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19. Georgia Guidestones

The imposing granite slabs of the Georgia Guidestones stand nearly 20 feet tall and have loomed above Elbert County farmland since 1980. The monument consists of six blocks that collectively weigh an impressive 237,746 pounds. The stones are inscribed with various homilies ranging from an exhortation to limit world population to 500 million to a plea for “fair laws and just courts.” Furthermore, the inscriptions are engraved in eight different languages.

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The stones were commissioned from the Elberton Granite Finishing Company by someone calling themselves Robert C. Christian – although he admitted that this was a pseudonym. In 2009 Wired magazine quoted Elberton Granite’s Joe Fendley as saying that he thought Christian was a “nut.” He attempted to discourage him with a ridiculous quote which Christian promptly accepted and the structure was built. It was erected because the latter apparently wanted a monument that would provide guidelines for the human survivors of some future cataclysmic event.

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18. Hemet Maze Stone

Hike through the San Jacinto Valley – a few miles west of the city of Hemet in California – and you’ll come across a massive boulder with an intriguing pattern carved into the stone. It’s known as the Hemet Maze Stone and the motif does indeed portray a puzzle-like maze around two by two feet in size. It was only discovered as recently as 1914 yet it is more than 3,000 years old.

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The Hemet Maze is classed as a petroglyph – a stone carving which has usually been made in ancient times. Dating rock carvings is no easy task, but this one’s age has been estimated by examining the encrustation that has gathered on its surface through the centuries. This gives an age estimate of between 3,000 and 4,000 years. However, we know neither who carved this enigmatic maze nor why they did so.

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17. Bighorn Medicine Wheel

The Bighorn Medicine Wheel is located high in the mountains in the remote depths of Wyoming’s Bighorn National Forest. It consists of a circle of white limestone rocks 80 feet across and is laid out on the landscape with lines like the spokes of a wheel running from the circle’s centre to its perimeter. Amazingly, the structure is said to date back as far as 10,000 years or more.

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Although the wheel is believed to have been made by Native Americans, it has not been attributed to any single tribe – although several consider it to be sacred. According to a 1972 study by astronomer John Eddy, cairns around the its perimeter align with sunset and sunrise at the summer solstice, and some line up with various celestial bodies. Having said that, the Bighorn Medicine Wheel’s precise purpose remains a conundrum.

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16. Blythe Intaglios

The Blythe Intaglios lie about 13 miles north-east of the city of Blythe in California – not far from U.S. Highway 95. Set at the foot of the Big Maria Mountains, the intaglios are huge images etched directly into the rocky ground. Works of this type are also known as geoglyphs and the largest of the Blythe ones – representing a human figure – is 171 feet long.

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As well as human figures, the geoglyphs portray animals such as snakes, mountain lions and birds. Meanwhile, others feature unidentified creatures or geometric motifs. A man called George Palmer discovered them in modern times as his plane flew over them in 1932. There are six geoglyphs in the Blythe group – all within around 1,000 feet of each other. There is also no certainty as to who created these enigmatic images and their meaning or purpose remains unknown.

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15. Judaculla Rock

Judaculla Rock is a large soapstone boulder with a flat side which is covered in enigmatic carvings. It’s located in remote, mountainous territory close to the banks of Caney Fork Creek in Jackson County, North Carolina. Etched into the malleable soapstone are an astonishing 1,548 symbols and patterns of various kinds. The rock also bears evidence of quarrying activity and the carving out of bowls.

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The motifs carved into the stone include stick figures, deer tracks, a winged symbol and a circle surrounding a cross. Archeological investigation has dated the marks left by cup-making to the Late Archaic era – which ran from around 8000 to 1000 B.C. The stone had a special significance to for the Cherokee people and experts believe the carvings are a representation of their world.

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14. America’s Stonehenge

America’s Stonehenge – previously known as Mystery Hill until its renaming in 1982 – consists of an array of large boulders and stones arranged into various types of structure. The site extends for some 30 acres and is set within the town boundaries of Salem in New Hampshire. It’s a popular tourist destination said to be favored particularly by New Agers – perhaps attracted by its resemblance to the real Stonehenge in England.

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There are those who have asserted that the stone edifices at America’s Stonehenge date back to pre-Columbian times, but this theory has been discounted by experts. In fact, it’s now generally believed that some of the structures at the site were erected in the 18th and 19th centuries by farmers. What’s more, many archeologists believe that one William Goodwin – who bought the site in 1932 – may have been the mystery builder of much of the American Stonehenge.

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13. Miami Circle

The Miami Circle is right in the downtown section of the Floridian city and it is indeed a perfect circle that’s made up of 600 post holes hewn into limestone rock. It’s the only archeological site of its kind in the eastern states of the U.S. The circle of post holes is 38 feet across and within it are 24 depressions cut into the rock.

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The circle is set at the mouth of the Miami River and was discovered during an archeological survey after an apartment building on the site was demolished in 1998. Using radio carbon dating of wooden remnants at the site, researchers dated the site to between 1,800 and 2,000 years ago. However, some academics have questioned the Miami Circle’s authenticity. And while other experts believe the site was created by the Tequesta tribe, its true purpose remains elusive.

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12. The Great Serpent Mound

Set in Adams County by the Ohio Brush Creek, the Great Serpent Mound is a curving earthwork extending for 1,348 feet. Seen from above, its resemblance to a huge snake is unmistakable. The mounds are between one and three feet in height and up to 25 feet across. Identification of the mound’s builders is hindered by the fact that no archeological artifacts have ever been discovered at the site.

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Experts have proposed two theories as to the Great Serpent Mound’s origins. The first is that it may have been built by the Adena people in around 320 B.C. The second proposition has it that people from the Fort Ancient Culture created the mounds much later in about 1070 A.D. Indeed, a fierce debate within the world of archeology continues to this day as to the origins of these mysterious earthworks.

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11. Mesa Verde Cliff Palace

The Cliff Palace is located in the Mesa Verde National Park and it’s a quite extraordinary series of structures built into the contours of monumental rock formations. The National Park – covering more than 50,000 acres – is home to over 5,000 archeological sites and the Cliff Palace is the best known of those. The Ancestral Puebloan people built and lived in these buildings – some 600 of which exist today.

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The Ancestral Puebloans constructed the dwellings from around 1190 A.D. probably as protection from increasing hostilities between different tribes in the region. Experts believe most of the structures were built over a period lasting just a couple of decades. The Ancestral Puebloans deserted these homes in around 1300 for reasons that are not entirely clear. But researchers have speculated that various factors may have been involved in the abandonment: including over-population, changes in climate and conflict with other tribes.

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10. Waffle Rock

Waffle Rock is set in West Virginia’s Randolph County by the shores of Jennings Randolph Lake – a manmade reservoir. When the Potomac River was dammed in the 1930s, the rock was saved from the rising waters and moved to its present position. And you only need to look at the strange pattern on this unusual rock to understand why it got its name. The criss-cross lines make it look for all the world much like a waffle you’d eat for breakfast.

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So what caused the decidedly weird patterns on the face of this rock? Conspiracy theorists have had a field day with it and claimed that the boulder was created by everything from giant lizards to aliens. Others have theorized that Native Americans carved the markings on the boulder. But the truth is a little less exotic; geologists assert that natural processes starting as long ago as 300 million years created the strange pattern.

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9. Spider Rock

Arizona’s Canyon de Chelly National Monument is home to Spider Rock – a peculiar feature that soars some 750 feet skywards from the ancient landscape. The land around the sandstone rock belongs to the Navajo people and this territory has been occupied by various tribes for around 5,000 years. But the question is: how was this extraordinary geologic formation created? Well, in 2017 the Arizona Highways website put that very question to geologist Harold Pranger of the National Park Service.

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Pranger explained, “Spider Rock at one time – many thousands to perhaps even hundreds of thousands of years – was connected to the ridge between the main Canyon de Chelly and Monument Canyon. The hillslope and stream erosion processes worked at different rates along that ridge, obviously at a slower rate right at Spider Rock. The differential erosion left this tower that is now called Spider Rock behind.” So, there’s your answer.

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8. Winnemucca Petroglyphs

The Winnemucca Petroglyphs were revealed to the modern world when Winnemucca Lake dried up in the 1930s. The rock carvings are in the north-west of Nevada on the borders of Pershing and Washoe counties – within the bounds of the Pyramid Lake Indian Reservation. And a number of boulders at the western end of the lake bed feature ancient carvings.

Image: Larry V. Benson, U.S. Geological Survey/{{PD-USGov-USGS}}

These Winnemucca Petroglyphs include geometric motifs, carvings that look like trees and flowers, and in one example a complex diamond design. They range from around eight inches to three feet across. Analysis using radio carbon dating has confirmed that the lake’s water level between 14,800 and 10,500 years ago was low enough to allow carving. This makes these petroglyphs the most ancient discovered in North America, but their meaning remains unknown.

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7. Cahokia Mounds State Historic Site

Just across the Mississippi River from St. Louis, you’ll find the Cahokia Mounds State Historic Site. This pre-Columbian land covers an area of some 2,200 acres and includes around 80 separate mounds. These are the remains of an ancient city whose boundaries actually meant it was larger than the site that remains today. And in ancient times, the city apparently covered almost 4,000 acres and included around 120 mounds.

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These man-made mounds are all that remains of this large conurbation which was built and occupied from about 1050 A.D. However, evidence of human occupation of the site dates back as far as 1200 B.C. The city consisted of a sophisticated network of public spaces, homes and ceremonial areas connected by paths. The metropolis was populated by a people that modern researchers call Mississippians who lived across wide swathes of North America. But the site was abandoned in about 1300 A.D. for reasons that are still open to speculation.

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6. Fort Mountain Wall

Set in Georgia’s Fort Mountain State Park, this ruined wall was built with rough stones blocks and extends for some 855 feet along the heights of Fort Mountain. The wall has a zigzag formation and at one point in its stretch there’s a tumbledown gateway. The stones that were used to build it were obtained from the surrounding landscapes. Furthermore, some weird and wonderful tales swirl around this ancient stone wall.

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One story even claims that it was built by Madoc – a Welshman who allegedly sailed to the United States in 1170 and built a series of fortifications there. However, a 1956 study by University of Georgia archeologists came to the more realistic conclusion that the wall “represents a prehistoric aboriginal construction whose precise age and nature cannot yet be safely hazarded…” To date, no one has been able to come up with a clear explanation of who built the wall and why they did.

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5. Aztalan Mounds

These mounds form part of the Aztalan State Park in Wisconsin’s Jefferson County and are the remains of a great city from 1,000 years ago. People of the Mississippian culture founded this city in around 1000 A.D. and its main remaining features are the monumental mounds that dot the site. The city’s builders were part of a widespread trading civilization which apparently stretched all the way from the Gulf Coast to the Great Lakes.

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The Mississippians built their homes around wide plazas which probably had some kind of ceremonial purpose. The large mounds have a flat-topped pyramid form and likely served as both ritual and defensive structures. After hundreds of years of occupation the city fell into decline sometime during the 13th century and was abandoned. No one is certain why this was so, but possible explanations have included environmental degradation and warfare.

Image: via New England Historical Society

4. New England Stone Chambers

You’ll find mysterious stone structures right across New England – with one estimate putting their number at around 800. There’s controversy about the true history of these chambers with a number of competing theories. Some say that the stone structures were actually built by some of the first Europeans to settle in New England and used for storage.

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Other experts assert that these stone buildings were erected by Native Americans before New England was settled by Europeans. And yet others believe that the structures were built by mooted European travelers to America as far back as the Bronze Age. Experts generally regard that last theory as extremely unlikely. This therefore leaves the competing ideas that the chambers were built by early European settlers or Native Americans. However, it seems that the jury remains out on that controversy.

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3. Chaco Canyon

Chaco Canyon is the centerpiece of New Mexico’s Chaco Culture National Historical Park. The location is home to the most extensive set of pre-Columbian buildings north of Mexico and includes 15 different archeological sites. Incredibly, some of the buildings at Chaco Canyon remained the largest ever erected in North America right up to the 19th century. There are experts who believe that the buildings of Chaco Canyon may have been used for ritual purposes only rather than as everyday dwellings.

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The Ancestral Puebloans built these structures and it was a major site for those people from around 900 to 1150 A.D. Experts have noted that many of the buildings are aligned with astronomical cycles – suggesting they may have had a devotional purpose. For reasons that are unclear – although drought may have played a part – the Ancestral Puebloans had abandoned the Chaco Canyon site by about 1150.

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2. Poverty Point

Poverty Point World Heritage Site is located in the north-east of Louisiana – not far from the village of Epps and adjacent to the banks of the Bayou Macon. The site includes a series of earthworks in the shape of mounds and ridges set round a large public space and extending over some 345 acres. For reference, the prehistoric structures were built from around 1700 to 1100 B.C.

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It was people from what is known as the Poverty Point culture who built these monumental mounds as long as 3,700 years ago. But what was the purpose of these impressive earthworks? That’s a question which has exercised archeologists for years. Experts are unsure if these mounds were a permanent city or whether they were perhaps only used on ceremonial, perhaps religious, occasions.

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1. Horseshoe Canyon

Horseshoe Canyon is set in a far-flung district of Utah and its renowned for the intriguing images painted on to the rock walls there. The most outstanding examples of these pictographs – painted in a style known as Barrier Canyon – are found in what is called the Great Gallery. And researchers have found other such images in Colorado and Arizona as well as in Utah.

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Experts believe that it was the nomadic hunter-gatherers of the Desert Archaic culture who created these beguiling images at the Great Gallery. Some experts have dated these pictographs to between 400 and 1100 A.D., although evidence of Paleo-Indian occupation of Horseshoe Canyon goes as far back as 9000 B.C. In fact, some believe the Great Gallery images may actually be around 7,000 years old but the exact dates of creation remain a matter of debate. And the significance or meaning of the artworks is unknown.