The Glen Helen Nature Preserve is a nature reserve immediately east of Yellow Springs, Ohio, United States. The initial 700-acre parcel was given to Antioch College by Hugh Taylor Birch in memory of his daughter Helen Birch Bartlet in 1929, and is the largest private nature preserve in the region. About The Glen is immediately adjacent to the main Antioch College campus (which itself contains restored natural areas managed by The Glen) and stretches in land area for . Together with the of the John Bryan State Park and the of the Clifton Gorge State Nature Preserve, the area comprises a river corridor of over 2,100 contiguous acres that has been rated "exceptional" by the Ohio Department of Natural Resources for its cleanliness and biodiversity. The preserve was designated a National Natural Landmark in 1965. The patches of land now included in Glen Helen previously had a number of different uses. While some were always natural, other areas were farmed, some grazed, and some extensively logged. The oldest trees in the Glen might be 400 years old, but there are many newer areas of forest 90 years old or younger. The Glen is actively managed to weed out non-native invasive species of plants like bush honeysuckle and Japanese stiltgrass; about 30 to 40 acres a year of honeysuckle are cleared. Those areas are then planted with native species like baby spicebushes, sumac, goldenrod, and sedge, which helps return the land to its original state and keeps the invasive species at bay. The Glen features more than twenty miles of publicly accessible trails and includes 2.5 miles of the National Scenic Little Miami River, regionally significant stands of old-growth forest, a distinct rock column known as Pompeii's Pillar, ecologically reclaimed farm land, the Orators Mound (a Adena burial mound), and the Yellow Spring, for which the town is named. The preserve was a learning laboratory for Antioch College, supporting academic offerings as well as faculty and student research, and also offering a wide variety of public programs and outreach to the wider Miami Valley region. The Glen had a long-time "friends" organization known as the Glen Helen Association ("GHA"). The roots of the GHA came about in 1960, with ultimately-successful efforts to save the Glen from a proposed highway bypass and then a sewer line. The GHA became an official nonprofit organization in 1979, with the continuing mission of helping to