The Nass Lake occurrence is located on a ridge 2.5 kilometres due west of Nass Lake, about 146 kilometres north-northeast of the community of Stewart. Dawson and Ryan identified the occurrence during reconnaissance of the Groundhog coalfield in 1991, and trenched and sampled the location (Trench BB90006, Dawson and Ryan, 1992; Geological Survey of Canada Open File 2555). The coal seam is 0.5 metre thick and the coal rank is semi-anthracite based on the vitrinite reflectance value of 2.78 RoMax.

Structural deformation is intense in this area (Geological Survey of Canada Open File 2555; Geological Survey of Canada Bulletin 577; and Geological Survey of Canada Map 2037A). At the occurrence site, the strata are folded into tight anticline and synclines; axial planes strike about 305 degrees and dips are near vertical dips (Cross section QQQ-RRR, Geological Survey of Canada Bulletin 577.)

The Nass Lake trench is in rocks mapped by Evenchick and Thorkelson (Geological Survey of Canada Bulletin 577) as Jenkins Creek assemblage, a nonmarine assemblage of Aptian to Albian (Lower Cretaceous) age. The Jenkins Creek assemblage includes mudstone, siltstone, sandstone and rare conglomerate and coal. Fossil plants are abundant.