Ice age glaciers played an essential role in shaping Yosemite’s landscape. Most of this ice had melted away due to natural warming by about 10,000 years ago. During a more recent cold period called the Little Ice Age, small glaciers formed below the highest peaks. Currently, two remain: the Maclure glacier and the Lyell glacier (shown). These ice bodies are important to local ecosystems because they provide a year-round supply of cold water to the Lyell Fork of the Tuolumne River, especially during the late summer and fall after the winter snowpack has melted. Image courtesy of the US National Park Service.