All of this info is from the website below:

http://www.dcnr.state.pa.us/forestry/oldgrowth/index.aspx

Welcome to the website for the Auto Tour of Old Growth Forests. Located primarily in the north-central part of Pennsylvania, the twenty sites on the Tour represent many different ecosystems, not only deep classic "big tree" forests. Most of the sites are within what is known as the Lumber Heritage Region, the 15 counties from which most of the timber resources were extracted in the 19th and early 20th centuries. Much of this area has now once more become a heavily wooded area, with over 2.5 million acres of Federal and State forests.
Learn more about what old-growth means and see how and why these particular sites were chosen for the tour. We'll explain the principles on which those choices were based and some of the history of Pennsylvania's magnificent forests.
Choose an Old Growth area from the map above of from the links below