July 16, 2015 5:47 AM EDT

WACO MAMMOTH

The Texas site (right) is home to remains of the Western camel, giant tortoise, saber-toothed cat and Columbian mammoths–which date back more than 65,000 years.

BASIN AND RANGE

The Nevada province is home to one of the largest collections of prehistoric rock carvings as well as Michael Heizer’s City, one of the world’s largest sculptures.

BERRYESSA SNOW MOUNTAIN

For at least 11,000 years, Native Americans have inhabited the California region, which boasts a large concentration of threatened species.

This appears in the July 27, 2015 issue of TIME.

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Write to Olivia B. Waxman at olivia.waxman@time.com.

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