See these links to learn more about the trails in Western Pennsylvania:

Friends of the Riverfront www.friendsoftheriverfront.org

Great Allegheny Passage (GAP)
www.atatrail.org

Montour Trail Council
www.montourtrail.org

Nine Mile Run Watershed Organization  
www.ninemilerun.org

Potomac Heritage National Scenic Trail
www.nps.gov/pohe/

Regional Trail Corporation
www.youghrivertrail.org

Steel Valley Trail
steelvalleytrail.org