Spires of limestone tufa rise from the shores of California’s Mono Lake. Tufa form when underwater springs rich in calcium meet lake water rich in carbonates, forming calcium carbonate, or limestone. The limestone precipitates in layers over time and can grow more than 30 feet (9 meters) high. Mono Lake’s tufa are particularly dramatic because water diversions have significantly lowered the lake’s level, exposing more of the columns.

(Photograph shot on assignment for, but not published in, the National Geographic special publication, Our Threatened Inheritance, 1982.)