Colonel Denning State Park is a 273-acre Pennsylvania state park in the Doubling Gap of Blue Mountain, surrounded by Tuscarora State Forest and centered on mountain recreation around the small man-made Doubling Gap Lake. Named for William Denning, a Revolutionary War veteran who served as a sergeant near Carlisle and developed a method of making lighter wrought-iron cannons, the park formally opened in 1936 after many facilities were built by the Civilian Conservation Corps in the 1930s. Its compact setting supports hiking, camping, picnicking, swimming, fishing, and hunting, with 18 miles of trails and access to the Tuscarora Trail.