Petersen Glacier lies in a cirque high above the north fork of Cascade Canyon in Grand Teton National Park, Wyoming, at about 10,000 feet. Named for early mountaineer Frank Petersen, who climbed Grand Teton in 1898, it reflects both the region’s glacial past and its early climbing history. The glacier formed during the Little Ice Age, roughly 1350 to 1850, and has been retreating since the mid-19th century. Its meltwater once carried rock flour that gave nearby Mica Lake a vivid turquoise color. No longer visible in satellite imagery, it may have disappeared entirely.