National Park Mystery Photo 16 Revealed: Yosemite Granite, Polished To a Sheen By Glaciers

The high country of Yosemite National Park has been richly polished by glaciers. Top photo, QT Luong/www.terragalleria.com/parks, used with permission, bottom photo Kurt Repanshek.

There I was, standing on a shelf of rock that borders Cathedral Lake in Yosemite National Park with Cathedral Peak and other crags lining the horizon, and I couldn't take my eyes off the ground.

What I was focusing on, of course, was a rust-hued patch of granite that had been buffed to a sheen with some serious "glacial polish." As any first-year geology student can explain, some granite surfaces in the High Sierra were "polished" by glaciers carrying pebbles, small rocks, and other grit that ground down the underlying granite to a smooth, and in some cases shiny, surface.

QT Luong, who has documented all 58 "national parks" with his photographic skills, and who appeared in Ken Burns' documentary, The National Parks: America's Best Idea, captured large patches of polished granite with Cathedral Lake in the background when he was in Yosemite, while my photo focused tightly on one particularly colorful patch.

The next time you find yourself in Yosemite, be sure to spend at least a little time looking at the ground, particularly when you walk the granite domes that line the Tioga Road or if you manage to hike all the way to the top of Nevada Fall. According to the National Park Service, "The corridors of the Merced River and South Fork Merced River contain some of the best evidence of glacial processes in the Sierra Nevada, such as glacial erratics, moraines, rouches mountonnées, and striations, as well as some of the best examples of glacial polish in the United States." (my emphasis)