Grannyknot--Presumably this is what is known as Anakeesta or "hot" rock. when laid bare and exposed to the elements it leaches out with bad results. There are numerous examples within the Park. In the aftermath of the completion of the Newfound Gap Road, some of the streams on the N. C. side which got leachate from the parking lot at the Gap suffered mightily for years. Indeed, Kephart Prong (then known as Mud Creek, perhaps from so much siltation) was so badly affected that the CCCs eventually shut down the fish hatchery located there. In the aftermath of a massive flood and landslide (could have been 1950 but I don't remember the date off the top of my head) Alum Cave Bluffs Creek was devoid of trout for many years. It is still marginal for them, at best. I briefly cover these two examples in my book, and of course hot rock was originally a key factor in stopping construction on the Road to Nowhere (one time where it did some good). I'm no geologist, but I think the Anakeesta Formation, which ranges through much of the Smokies, is what is in play here.