Popo Agie Wilderness is one of the more popular climbing and hiking destinations, and an estimated 200 different climbing routes are located within the peaks that surround the cirque. There are over 500 lakes in the forest, and of streams and rivers. The Clarks Fork of the Yellowstone River is federally designated as a Wild and Scenic River for through the forest, with cliffs towering up to as the river winds through a gorge. The forest is on the eastern slopes of the Continental Divide, and the rivers flow into the Atlantic Ocean basin. Glaciology According to the U.S. Forest Service, Shoshone National Forest has the greatest number of glaciers of any National Forest in the Rocky Mountains. The forest recreation guide lists 16 named and 140 unnamed glaciers within the forest, all in the Wind River Range. Forty-four of these glaciers are in the Fitzpatrick Wilderness, centered around the highest mountain peaks. However, the state water board for Wyoming lists only 63 glaciers for the entire Wind River Range, which includes glaciers in adjacent Bridger-Teton National Forest. Researchers claim that for most of the period that glaciers have been known to exist in the forest, that they have been in a state of general retreat, with glacial mass losses of as much as 25 percent between the years 1985 and 2009. Reversing the growth of mid-latitude glaciers that occurred during the Little Ice Age (1350–1850), there has been a worldwide reduction of mountain glacial ice since, with some regions losing as much as 50 percent of their peak ice cover. This can be correlated by examining photographic evidence of glaciers taken over time even with an absence of other means of documentation. The behavior of the glaciers of Shoshone National Forest is consistent with this pattern. In one study of Dinwoody and Gannett Glaciers, during the period from 1958 to 1983, the thickness of these glaciers was reduced , respectively. Gannett Glacier, on the northeast slope of Gannett Peak, is the largest single glacier in the U.S. Rocky Mountains. It has reportedly lost over 50 percent of its volume since 1920 with 25 percent of that occurring between the years 1980–1999. Upper Fremont Glacier has been studied more than any other glacier in the Wind River Range. Scientist have obtained ice cores from the Upper Fremont Glacier and found that there have been measurable changes in the atmosphere over