were subsequently glaciated in the Cispus River valley; whether Old Snowy Mountain is a vent of Goat Rocks or an independent volcano remains unclear. Hornblende andesite can also be found on top of the highest point in Goat Rocks, Gilbert Peak. Hogback Mountain, a shield volcano north of Goat Rocks and south of White Pass, was identified by Siebert et al. (2010) as a satellite vent of Goat Rocks. Rising in elevation, it erupted more than of olivine basalt and basaltic andesite from the end of the Pliocene through the early Pleistocene. Eruptions from Goat Rocks formed a spread-out volcanic field populated by small lava domes to the north, with dimensions of by . Goat Rocks is now classified as an extinct volcano, as its most recent eruptive activity was during the Pleistocene. The last eruption from the Goat Rocks complex occurred around 115,000 years ago. It was an effusive lava flow known as the Clear Fork Lava. The flow was primarily composed of dacite and flowed 12 km (7.5 mi) along the White Pass Highway. The flow has an estimated volume of 0.55 km3 (0.13 mi3). Wilderness Land surrounding Goat Rocks was first protected by the United States Department of Agriculture in February 1931, when approximately was set aside for preservation. In 1935, this was increased to of land, then to in 1940. In 1964, the United States Congress created the Goats Rock Wilderness as part of the National Wilderness Preservation System, delegating its management to the United States Forest Service. Since additional land was incorporated in 1984, it now encompasses between Mount Rainier and Mount Adams, straddling the Gifford Pinchot and Okanogan-Wenatchee national forests. It is bordered by the Yakama Indian Reservation to the southeast. The wilderness ranges from in elevation, featuring alpine tundras with glaciers, small lakes, and ponds, as well as 15 different routes that amount to of trails. One of these trails constitutes the highest segment of the famous Pacific Crest Trail in Washington, running for north–south through the middle of the wilderness area. Because this route is located at such a high elevation, its hikers may experience violent storms that could be dangerous for unprepared parties. Much of the wilderness is located above the timberline, offering views of alpine scenery. Climate and wildlife Weather within the Wilderness varies due to the mountains acting as a barrier for both weather and temperature. The Cascade Range