 Once one of the largest glaciers in the park, the surface area of Sperry Glacier has retreated 75 percent since the mid-19th century.2005 measurements of the surface area of the glacier resulted in an estimated area of , whereas the glacier is estimated to have covered an area of at the end of the Little Ice Age in the mid-19th century.The glacier lost almost 35 percent of its surface area between 1966 and 2005.