To the western breaks. Our aim was to look for green agatized wood, but we hiked all over the place.

There were fragments of bone scattered through the arroyos—even part of a jaw, you could see the tooth sockets. At the base of the cliffs I spotted broken antlers, picked them up…and they were stone. I examined them with a hand lens and found, on one, the tiny, parallel, transverse scars left by the incisors of a Pliocene mouse or vole.

Those delicate tooth marks are slightly over two million years old.

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