The Winds are composed primarily of a granitic batholith which is granite rock formed deep under the surface of the Earth, over one billion years ago. Over hundreds of millions of years, rocks that were once covering this batholith eroded away. As the land continued to rise during the Laramide orogeny, further erosion occurred until all that remained were the granitic rocks. The ice ages beginning 500,000 years ago began carving the rocks into their present shapes. Within the Winds, numerous lakes were formed by the glaciers and numerous cirques, or circular valleys, were carved out of the rocks, the most well known being the Cirque of the Towers, in the southern section of the range. Shoshone National Forest claims that there are 16 named and 140 unnamed glaciers just on the east side of the range for a total of 156, with another 27 reported by Bridger-Teton National Forest for the western slopes of the range. Several of these are the largest glaciers in the U.S. Rocky Mountains. Gannett Glacier which flows down the north slope of Gannett Peak, is the largest single glacier in the Rocky Mountains of the U.S., and is located in the Fitzpatrick Wilderness in Shoshone National Forest.