The 45 to 60-metre thick Sunnyside limestone of the Upper Triassic Hedley Formation (Nicola Group) outcrops in an arcuate manner on the west, south and east slopes of Nickel Plate Mountain, just east of Hedley. This unit is enclosed within a westward dipping sequence of argillites, siltstone and impure limestones intruded by dioritic sills of the Early Jurassic Hedley Intrusions and to the south by granodiorite of the Middle Jurassic Cahill pluton.

The Sunnyside limestone member is composed mostly of thin to thick-bedded, light bluish grey, medium-grained limestone that is frequently siliceous and contaminated by chert. A quarry on the west face of Nickel Plate Mountain, just above the granodiorite contact, exposes a 9-metre thick bed of purer limestone underlain by impure limestone containing numerous sills and overlain by siliceous limestone with chert nodules. A chip sample of the purer bed contained 52.43 per cent CaO, 1.37 per cent MgO, 2.00 per cent SiO2, 0.29 per cent Al2O3, 0.29 per cent Fe2O3 and 0.01 per cent sulphur over a thickness of 9 metres (Canada Bureau of Mines Report 811, page 202, Sample 58).

Between 1926 and 1937, limestone was quarried 150 metres up the west face of Nickel Plate Mountain to supply lime for the mill at the Nickel Plate gold mine (092HSE038). Approximately 2385 tonnes of limestone were quarried during this time.