Ancient granite outcrops reflect in the still water of Sylvan Lake in South Dakota’s Custer State Park as a lone fisherman awaits a nibble. Geologists calculate that the park’s granite, into which the sculptures at nearby Mount Rushmore were carved, are about 1.7 billion years old, making it some of the oldest rock in North America.

(Text adapted from and photograph shot on assignment for, but not published in, “Big, Bad, and Beautiful,” May/June 1996, National Geographic Traveler magazine)