The Wind River Mountains form the Continental Divide, sending water into the Columbia, Colorado, and Missouri River watersheds. Their rocks are more than one billion years old, though the mountains rose during the Laramide Orogeny eighty to thirty-five million years ago, and several ice ages beginning around five hundred thousand years ago carved them into their present shapes. Numerous glaciers with permanent ice still exist. The range is bounded by Union Pass on the north and South Pass on the south, extends one hundred miles long and thirty miles wide, is often called "The Winds," and includes more than thirteen thousand named lakes, more than six hundred miles of hiking trails, three designated wilderness areas—Bridger, Fitzpatrick, and Popo Agie—and forty named peaks above thirteen thousand feet. Major glaciation retreated around fifteen thousand years ago, though glacial melting continues, and signs of human occupation have been found at eleven thousand feet dating back more than eleven thousand years. Union Pass, first documented by Wilson Price Hunt in eighteen eleven, was used by Native Americans and early mountain men to cross between the Green, Snake, and Wind River valleys, and U.S. Army Captain William F. Raynolds named it in eighteen sixty. Gannett Peak, at thirteen thousand eight hundred nine feet above sea level, is Wyoming’s highest peak and the apex of the central Rockies, and was named after Henry Gannett in nineteen oh six. Fremont Peak, at thirteen thousand seven hundred forty-five feet, is the range’s second-highest peak and was named for John Charles Fremont, who climbed it in eighteen forty-two with Kit Carson as guide. Mount Bonneville rises twelve thousand five hundred ninety feet and was named after Benjamin Bonneville. Temple Peak rises twelve thousand nine hundred seventy-seven feet in the southern Wind River Mountains and appears sharply pointed from the northwest but rounded from the south. South Pass, first documented by Robert Stuart in eighteen twelve, offered Oregon Trail emigrants in the mid-eighteen hundreds an unexpectedly easy crossing of the Continental Divide. In the southern Winds, the Cirque of the Towers is a popular technical climbing destination where granite mountains form an almost circular valley carved by glaciers that retreated about fifteen thousand years ago, and the area was named by Orrin Bonney in nineteen forty-one.