Two hours east of San Diego, across the vast expanse of Anza-Borrego Desert State Park, lie countless ancient rock circles in the remote terrain, their purpose unknown and a mystery to this day.

Primarily found on rocky terraces and ridges within California’s largest state park, the manmade circles measure about 8 to 10 feet across. They’re made up of small rocks placed next to each other, ranging from 4 to 10 inches. Some circles are clustered next to each other, while others are on their own.

The intrigue, though, lies in the sheer number of them. “One of the archaeologists in the ’80s went out and did his best estimate in counting, and he counted 500 in 9 square miles,” Hayley Elsken told SFGATE in a phone call. Elsken is the associate state archaeologist for the Colorado Desert District of California State Parks.

There are hundreds to thousands of these ancient manmade rock circles within Anza-Borrego Desert State Park.

Since Anza-Borrego Desert State Park is over 620,000 acres, or more than 935 square miles, Elsken said there could be thousands scattered across the desert landscape.

While their exact age and purpose remain uncertain, one thing experts agree on is that their origin is Native American. 

The whole park is the ancestral homeland of the Cahuilla, Kumeyaay and Cupeno. Over 4,000 historic sites are found throughout the park, including villages, hunting and food processing areas. There are also numerous petroglyphs and pictographs, as seen on the Ehmuu-Morteros Trail in Little Blair Valley Cultural Reserve.

The highest concentration of rock circles is in the southern portion of the park, Elsken said, which is

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