The highest peak of its namesake Twin Range, South Twin Mountain is also the eighth-highest mountain in New Hampshire according to the AMC list and the ninth-highest on the New England Hundred Highest list. The summit rocks offer long views in all directions, including the highest mountains in New Hampshire: the nearby Franconia Range to the west and southwest, and the Presidential Range off to the northeast. The view also includes the entire Pemigewassett Wilderness and the Sandwich Range beyond it.

The namesake town of Twin Mountain lies nearby to the north. This name is written in the singular, implying that South Twin and North Twin are a single mountain, but the USGS and all maps list the two peaks as separate mountains.

In the decades prior to 1911, the unregulated logging practices of private timber companies in the White Mountains had resulted in a damaged landscape susceptible to both fire and flood. Fires had burned thousands of acres, and flash floods affected the water power necessary to the mills of major industrial centers downstream, such as Manchester, New Hampshire, and Lowell, Massachusetts. Concerns over losses to industry, business, and tourism, and the growing conservation movement led to citizen action. The Appalachian Mountain Club (AMC) and Society for Protection of New Hampshire Forests (SPNHF) spearheaded an effort to ensure the permanent protection of the White Mountains from further depredation. After years of lobbying and intense public pressure, Senator John Weeks of Massachusetts, a native of Lancaster, New Hampshire, introduced legislation that became known as the Weeks Act. The Weeks Act was passed by Congress in 1911, appropriating 9 million dollars to purchase 6 million acres of land in the Eastern U.S. In turn, this led to the creation of the White Mountain National Forest (WMNF) in 1918, and twenty-one other national forests throughout the north and southeast. Many of the groups who were instrumental in the passage of the Weeks Act, including the SPNHF and the AMC, are still active today, and the WMNF has grown from 7,000 acres to almost 800,000. Today, the reforested mountains and hillsides supply forest products and provide magnificent recreational opportunities while maintaining healthy watersheds and ecosystems.

South Twin is a fairly popular day hike from the north, usually after passing over North Twin but also via the Gale River Trail to Garfield Ridge. The mountain is also commonly climbed as part of a longer hike after a night at Galehead Hut, located on a col to the west of the summit. The hut and the summit lie on the Appalachian Trail, so South Twin gets thousands of visitors each year.