Geologically speaking, the name Crater Lake is a misnomer. Technically, Crater Lake lies in a caldera, which is produced when the center of a volcano caves in on itself; in this case, the cataclysm occurred 6,600 years ago with the destruction of formerly 12,000-foot-high Mount Mazama.

Klamath Native American legend has it that Mount Mazama was the home of Llao, king of the underworld. The chief of the world above was Skell, who sometimes would stand on Mount Shasta, 100 miles to the south. A fierce battle between these two gods took place, a time marked by great explosions, thunder, and lightning. Burning ash fell from the sky, igniting the forest, and molten rivers of lava gushed 35 miles down the mountainside, burying Native American villages. For a week the night sky was lit by the flames of the great confrontation.

The story climaxes with Skell’s destruction of Llao’s throne, as the mountain collapsed on itself and sealed Llao beneath the surface, never again to frighten the people and destroy their homes. Although the lake became serene and beautiful as the caldera filled with water, the Klamaths believed that only punishment awaited those who foolishly gazed upon the sacred battleground of the gods.

The aftereffects of this great eruption can still be seen. Huge drifts of ash and pumice hundreds of feet deep were deposited over a wide area up to 80 miles away. The pumice deserts to the north of the lake and the deep ashen canyons to the south are the most dramatic examples. So thick and widespread is the pumice that water percolates through too rapidly for plants to survive, creating reddish pockets of bleakness in the otherwise green forest.

The eerie gray hoodoos in the southern canyons were created by hot gases bubbling up through the ash, hardening it into rocklike towers. These formations have withstood centuries of erosion by water that has long since washed away the loosely packed ash, creating the steep canyons visible today.

Wizard Island, a large cinder cone that rises 760 feet above the surface of the lake, offers evidence of volcanic activity since the caldera’s formation. The Phantom Ship, located in the southeastern corner, is a much older feature.

The lake is confined by walls of multicolored lava that rise 500–2,000 feet above the water. Although Crater Lake is fed entirely by snow and rain, the lake does contain a small amount of salts from surrounding rocks, but the salty water is replaced by purer rain and snow. The level of the lake fluctuates only 1–3 feet per year as evaporation and seepage keep it remarkably constant.

Another surprise is that while Crater Lake often records the coldest temperatures in the Cascades, the lake itself has only frozen over once since records have been kept. The surface of the lake can warm up to the 60°F mark during the summer. The deeper water stays around 38°F, although scientists have discovered 66°F hot spots 1,400 feet below the lake’s surface.

Rainbow trout and kokanee (a landlocked salmon) were introduced to the lake many years ago by humans. The rainbow can grow up to 25 inches long, feeding mainly on the kokanee; the kokanee do not exceed 15 inches. Some types of mosses and green algae grow more than 400 feet below the lake’s surface, a world record for these freshwater species. Another distinction is Crater Lake’s selection as the purest lake in the world by scientists who determined in 1997 that the water’s clarity extended down 142 feet.