The Upper Klappan coal occurrence is located in the upper headwaters of the Klappan River, 6 kilometres directly north of Nass Lake, and approximately 152 kilometres north-northeast of the community of Stewart. The Arctos (Mount Klappan) developed prospect (104H 021) is 13 kilometres west.

Showings in occurrence area are hosted by rocks mapped by Evenchick and Thorkelson (Geological Survey of Canada Bulletin 577) as the Groundhog-Gunanoot assemblage, the main coal-bearing unit of the Upper Jurassic-Lower Cretaceous Bowser Lake Group. The Groundhog-Gunanoot is a deltaic assemblage, consisting of sandstone, siltstone, and carbonaceous and calcareous sandstone, with minor conglomerate and coal. The beds in the Upper Klappan area are folded into synclines and anticlines with axial planes that strike about 135 degrees. Axial plane traces are locally bent, indicating at least two deformational episodes.

In 1981, Gulf Canada acquired the Mount Klappan property. They explored the Upper Klappan area (referred to as Little Klappan in 1982, then combined with an area to the south and renamed the Nass Area in 1983 and 1986) with aerial reconnaissance, ground mapping, and 18 trenches with a total length of 64.5 metres. Nine coal seams were identified with seam thicknesses varying from 0.86 to 3.96 metres (Coal Assessment Reports 111,710 and 722). Gulf used the term "Klappan sequence" for the main coal-bearing unit in the greater Mount Klappan area.

In 1991, Dawson and Ryan (Geological Survey of Canada 2555) trenched and sampled in three locations in the Upper Klappan area. Coal seam thicknesses at those trenches ranged from 0.40 to 5.8 metres, and vitrinite reflectance values ranging from 3.4 to 4.83 per cent RoMax (anthracite rank).

See Arctos (104H 021), located 13 kilometres west, for further discussion of the history of formation nomenclature of the Bowser Lake Group.