Miller Esker, also known as Jacksonville Esker and West Liberty Hogback, formed about 23,000 years ago when northwestern Pennsylvania was covered by a 100-foot-thick sheet of ice. As temperatures increased, melting ice carved a river-like tunnel within the glacier, and flowing water carried cobbles, sand, and gravel. When the glacier receded, this material was deposited along the tunnel’s path, leaving a serpentine mound that over thousands of years became covered with soil and vegetation. The 32-acre Miller Esker Natural Area includes what is likely the best-preserved esker in the state. Many eskers, including portions of Miller Esker outside the natural area, have been mined for sand and gravel deposits. Miller Esker is named after the Miller family, who have farmed the adjoining property for over 100 years and once grazed cows and picked blueberries along the esker. Immediately north of the esker lies a wetland created by the melting glacier, and other nearby glacial features include a kame delta, a lake plain, and various stream diversions.