Lyell Glacier lies on the northern slopes of Mount Lyell in Yosemite National Park and was identified by John Muir in 1871 as the park’s largest glacier and a major remnant of Sierra glaciation. Since the end of the Little Ice Age in the mid-19th century, it has changed drastically. By the mid-20th century, the former single glacier had split into two smaller ice bodies in Mount Lyell’s high cirques, and since 1883 its area has shrunk by as much as 70 percent. A 2013 study found that it no longer moves, making it better classified as an ice field, though it remains significant in Yosemite’s environmental history.