An irregular, north trending mass of Permian-Mississippian limestone of the Devonian to Triassic Harper Ranch Group, 3 kilometres in length and up to 2.5 kilometres in width, outcrops on the north side of the South Thompson River, 18 kilometres due east of Kamloops. To the east the limestone is overlain by sandstone and conglomerate containing clasts of andesitic to basaltic volcanics of the Upper Triassic Nicola Group. To the west the limestone contacts argillite and quartzite of the Harper Ranch Group. The limestone mass appears to be situated along the crest of an anticline plunging 20 degrees south. Bedding on the east limb of the fold strikes 020 degrees and dips 40 degrees east. Conodont sampling in the quarry on the south end of the deposit reveals the limestone is broken up into at least two sequences dipping 50 to 80 degrees southeast that are repeated by a fault on the west margin of the quarry. The quarry exposes a number of basaltic and lamprophyric dikes 0.15 to 3.0 metres wide striking 090 degrees and dipping 70 degrees north.

The mass is made up of fine to medium grained, light to dark grey limestone with abundant white to grey chert as nodules, irregular patches up to 0.6 metre wide, and as discontinuous bands 0.1 to 0.6 metre thick. The chert is more frequent near the margins of the deposit. A 60 to 90 metre wide central zone is relatively free of chert. Quartz tends to occur as fine, silty aggregates that form up to 50 per cent of the rock. The limestone in the quarry is commonly veined with iron carbonate (siderite) and cut by faults containing hydrous iron oxides (limonite). In places, the limestone grades up to 95 per cent CaCO3 within the quarry (John Wong, personal communication, 1989). A chip sample taken across a 91.4 metre thick section of purer limestone northeast of the quarry analysed 55.04 per cent CaO, 0.46 per cent MgO, 0.42 per cent SiO2, 0.09 per cent Al2O3, 0.07 per cent Fe2O3 and nil sulphur (CANMET Report 811, page 184, Sample 49).

Lafarge Canada Inc. began quarrying the south end of the Harper Ranch deposit in 1970 to supply an adjacent cement plant. In 1976, 23 percussion-drill holes totalling 1347 metres were drilled on behalf of Lafarge Canada Ltd. In 1993, a long-term mining plan was defined on behalf of Lafarge Canada Inc.

Remaining reserves are 6 million tonnes grading 50 per cent CaO and represents a 23 year supply at a current production rate of approximately 260,000 tonnes per year (Assessment Report 24554).