The Horn River Formation (also Horn River Shale) is a stratigraphic unit of Devonian (early Givetian to late Frasnian) age in the Western Canadian Sedimentary Basin.It is a thick sequence of marine sediments that was first described in outcrop on the banks of the Horn River, a tributary of the Mackenzie River, in the Northwest Territories (at the time District of Mackenzie) by Whittaker in 1922, and it takes its name from that river. In 1963 it was redefined in the subsurface of the Fort Nelson area of British Columbia (well Fort Nelson a-95-J/94-J-10) by F.F. Gray and J.R. Kassube. It is significant for its shale gas resources.