The Allegheny Portage Railroad was the first railroad constructed over the Allegheny Mountains. This inclined plane railroad operated between 1834-1854 and was considered a technological wonder in its day and played a critical role in opening the interior of the United States to trade and settlement. Allegheny Portage Railroad National Historic Site is located in southwestern Pennsylvania approximately 12 miles west of Altoona. Today's park covers 1249 acres. The main unit contains the Summit Level Visitor Center, the historic Lemon House, Engine House #6 Exhibit Shelter, the Skew Arch Bridge, picnic area and hiking trails. The Staple Bend Tunnel unit is located approximately 4 miles east of Johnstown, PA.