Lake Mead, the largest manmade reservoir in the country, is located on the site of an ancient Native American settlement called the Lost City. The settlement’s been underwater since the 1930’s, when the Hoover Dam was built thirty miles from Las Vegas. No one ever expected to see it again.

But now a severe drought, made worse by climate change, is sucking the water from the West’s rivers and lakes, and the surface of Lake Mead has dropped so low that the ancient city has reappeared.

Just goes to show, you never know when a lost civilization’s gonna make a comeback–or when a thriving one’s gonna drive itself to the brink of extinction. The gap between Lake Mead’s highwater mark, or “bathtub ring,” and the lake’s current level grows ever wider. Will we see the writing on the reservoir walls in time to keep our own cities from becoming lost?