The A-25-D well / Trutch Sulphur showing is located 1 kilometre west of the Alaska Highway, approximately 115 kilometres south of Fort Nelson and 35 kilometres south of the community of Prophet River.

The Trutch Sulphur showings are situated on dominantly lower Cretaceous silty marine mudstones of the Buckinghorse Formation (GSC Bulletin 328). Regional structures are characterized by north-northwest–trending box folds with wavelengths of a few kilometres (Lane et al. 1998).

Native sulphur was intersected in well A-25-D; 94G/15, a hole drilled for petroleum exploration. The well was drilled in a succession of evaporites, reefal carbonates and thin beds of clastic rocks of the Middle Devonian Elk Point Group. A drillstem test, conducted between 3189.7 and 3264.4 metres depth, intersected 6.1 metres of solid sulphur in the Keg River Formation.