Johnson Run Natural Area is a 216-acre nature preserve in Cameron County, Pennsylvania, set on a rugged, boulder-strewn plateau carved by steep-sided streams into broken, uneven terrain. It is especially important for preserving a remnant old-growth forest estimated at between 26 and 50 acres. This surviving stand of mature native woodland includes Eastern Hemlock and Eastern White Pine, with some white pines reaching nearly 4 feet in diameter at breast height. Within its deeply dissected landscape, the area protects an uncommon example of long-established forest.