From the trailhead sign:
The Forest Cathedral Natural Area contains one of the largest old growth forests of white pine and eastern hemlock in Pennsylvania. Many of these magnificent pine and hemlock trees now exceed three feet in diameter and approach 200 feet in height. Trees of this size are often over 300 years of age; dating to the era of William Penn, the first Governor of "Penn's Woods", and are often referred to as "William Penn Trees". It is perhaps fitting that this forest remains in the midst of an area which saw the greatest logging boom in the history of the Commonwealth - the period of the late 1800s, when thousands of acres of old growth forests were cut for the shipbuilding and constructions industries. The Forest Cathedral is registered as a National Natural Landmark and has been set aside for protection as a State Park Natural Area.