The Tetsa River phosphate occurrence is situated on the north side of the Alaska Highway, 2 kilometres northeast of the confluence of the Tetsa and North Tetsa rivers, about 21 kilometres east of Summit Lake (Fieldwork 1987, Figure 3-7-1, sample locality SB87-40; Open File - Phosphate Deposits in British Columbia).

The deposit is in the Early to Middle Triassic Toad Formation, part of the platformal to basinal sedimentary succession that makes up Ancestral North America (Geological Survey of Canada Map 1713A). The formation is composed of dark grey calcareous siltstone and shale, and minor silty limestone and very fine grained sandstone (Geological Survey of Canada Memoir 373, Map 1343A). Most lithologies are weakly to moderately carbonaceous. Phosphate-bearing beds occur in the lower and middle parts of the formation, an interval which varies in thickness from a few tens of metres to approximately 290 metres (Fieldwork 1987, page 401; Geological Survey of Canada Bulletin 247).

The Tetsa River showing consists primarily of a bed of pelletal phosphorite, 15 to 20 centimetres thick, in a 3.3-metres thick sequence of dark grey carbonaceous siltstone and limestone (Open File - Phosphate deposits in British Columbia). The siltstone also contains nodules of phosphate locally. The beds in the sequence, which range from 0.5 to 1 metre in thickness, are subhorizontal or dip gently westwards, and average 4.3 per cent P2O5. The pellets in the phosphorite, assumed to consist of fluorapatite (Geological Survey of Canada Bulletin 247, page 20), range in size from 0.05 to 0.15 millimetre. Most have a nucleus of quartz or, less commonly, carbonate. The matrix comprises quartz with minor calcite and very minor feldspar. Also present are rare phosphatized shell fragments and nodules.