Twenty thousand years ago, a glacier churned down Lee Vining Canyon. Hundreds of feet thick at the top of the canyon, the glacier reached its maximum extent at the site of what is now the US Forest Service ranger station, just west of Lee Vining.
It is now easier to picture this arm of what scientists call the Tioga glaciation thanks to a new US Geological Survey map showing its extent throughout the Yosemite region. Greg Stock, geologist for Yosemite National Park and one of the map’s authors, spoke at the Mono Lake Committee last month. To a packed room, he described the jumble of moraines, boulders, and rock striations that he and his colleagues deciphered to build the map.
But this latest map is based on more than work by Stock and his colleagues. It also draws on the efforts of an earlier generation of scientists. In other words, just as the Tioga glaciation isn’t the only glacial period in the Sierra Nevada’s past, the 2019 map is not the first map of the Tioga glaciation in the park. (more…)