Haynes Cave is one of the oldest caves within the Greenbrier River watershed in West Virginia. It sits within the complex hydrology of the historic Second Creek watershed in Monroe County. Haynes Cave has been the only contender against Organ Cave as the discovery site for Thomas Jefferson's Megalonyx jeffersonii. The lack of accurate records and the vagueness of the descriptions had left much room in doubt for the true location of the sloth skeleton. Jefferson wanted to link the bones with early reports of a giant lion in North America, but knew the fossil was incomplete. He chose, until further discovery, to restrict the name to "Great-Claw," for it was at the time the most distinguishing characteristic of the skeleton.