The monument's centerpiece is this 18sq mi caldera, within whose forested floor snuggle deep-blue Paulina and East lakes, a massive obsidian flow and numerous archeological sites. Beginning about a million years ago, the first of hundreds of volcanic eruptions created concentric fractures that, by 200,000 years ago, had collapsed to form the 5mi-wide caldera. A single large lake-much like Oregon's Crater Lake-filled the basin. Ten thousand years ago, even before smaller eruptions and lava flows had divided the lake in two, Native Americans were maintaining Stone Age camps in the crater. They quarried obsidian, the black volcanic glass used in making tools and weapons. Signposts mark several camps and quarries.Fur trapper Peter Skene Ogden apparently was the first visitor of European ancestry when he stumbled upon the lakes in 1826. The crater was named for Dr. John Newberry, a 19C railroad surveyor and scientist; Paulina Lake was named for a Paiute chief who made the caldera his hunting ground.