There was gold in them there hills…

The red clay formations called Las Médulas owe their angular character not to the shaping hands of nature but to those of gold miners—and not grizzled '49ers in grubby flannel and overalls, but 1st-century excavators clad in tattered tunics. When gold seams were discovered here in what's now northern Spain, the Romans who controlled the region created a clever system of tunnels and canals under the hills, through which they channeled water from nearby streams to build pressure that cracked away huge chunks of clay.
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