The Appalachian Mountains formed approximately 500 million years ago when continental collisions created towering peaks, some reaching up to 20,000 feet, and over time erosion created the rolling hills and forested mountains that surround Deep Creek Lake today. When the lake was created, it was largely devoid of aquatic life, but with the growth of submerged aquatic vegetation and the stocking of selected varieties of fish, it became a premier western Maryland fishing location where bluegill, northern pike, and bass now maintain self-sustaining populations. Streams and rivers in the region provide vital aquatic habitats, and the protected Youghiogheny Wild and Scenic Corridor is a key conservation area around the Youghiogheny River, whose waters and rocky rapids support wildlife including brook trout, river otters, and the hellbender, one of the world's largest salamanders. Other Garrett County valleys form still-water bogs, mountain peatlands covered by mats of spongy sphagnum mosses that face limited nutrients and extreme seasonal temperature fluctuations and support rare wild cranberries, bog copper butterflies, pitcher plants, and sundews. Some of these areas also contain frost pockets where cool air settles on calm nights and creates a climate much colder than surrounding areas, allowing northern species to take refuge there, including northern saw-whet owls, whose nesting locations in Maryland are rare. The surrounding mountain terrain also provides habitat for uncommon animals such as the fisher, a seldom-seen large weasel reintroduced to the region in the 70s after overharvesting and known for hunting squirrels, turkeys, and even porcupines in the trees. Together these waters, bogs, frost pockets, and mountain ridges form a rich mosaic of habitats for diverse and rare plants and animals.