Andrea felt the triceratops before she saw them. The huge animals rumbled across the rolling ground, half rhino, half porcupine, half armored panzer, sending tremors up through her hands and feet.

These floodplains looked flat, but that was only the tops of the bushes. Under the spiny branches, the dense, clay-like soil was cut by hundreds of creek-beds and dinosaur wallows. Andrea was lying in one of these arroyos, thankfully dry at the moment, holding a snakeskin full of ...