ELIZABETH, Pa. — Conrad Weiser, Environmental and Cultural Resources, Col. William Graham, U.S. Army Corps of Engineers Pittsburgh District Commander, Andrew Masich, Pennsylvania Historical and Museum Commission Chairman, and Brush Kish stand beneath the historical marker at the Elizabeth Locks. A historical marker recognizing the Monongahela River Navigation System as one of the nation's most historically successful river systems was dedicated June 18 at Locks and Dam 3, Monongahela River.