Begun in 1970, the entire project was a massive engineering feat that took eight years to complete. According to Wikipedia, water is pumped from nearby Nickajack Lake to a massive 528 acre reservoir atop Raccoon Mountain. In times of high electric demand, "water can be released from the reservoir through a tunnel drilled through the center of the mountain, driving electric generators in an underground hydroelectric plant".

Expect plenty of rocks and roots as well as alternate lines around larger features. While there are some beginner-friendly trails atop the mountain, they only makes up a small portion of the ~20-mile network. It's popularity among mountain bikers means many of the climbs are relatively gradual, often utilizing switchbacks on the steepest sections. You can begin this run at the Laurel Point parking lot, or at the smaller trailhead along the road.

Trail names like Megawatt, Live Wire, and High Wattage mirror the massive power plant that looms ominously in the background. At the point where Megawatt transitions into Grindstone Ridge, look for a phenomenal vista looking north to the Tennessee River. Prentice Cooper State Forest lies on the other side of the river and the iconic Pot Point Loop is another favorite among trail runners.

Sources: https://ultrasignup.com/register.aspx?did=60703 https://en.wikipedia.org/wiki/RaccoonMountainPumped-StoragePlant http://www.sorbachattanooga.org/raccoon-mountain