Pool in Marble Canyon, Arizona

Photograph by Walter Meayers Edwards

Beyond the roar of the Colorado River, a pool of silence. Discovering this hushed limestone sanctuary at Shinumo Wash in Arizona's Marble Canyon, members of a National Geographic expedition christened it Silver Grotto.

(Photo shot on assignment for "Retracing John Wesley Powell's Historic Voyage Down the Grand Canyon," May 1969, National Geographic magazine)