A mass of limestone of the Carboniferous or older Anarchist Group lies on the northeast slope of Thimble Mountain 10.7 to 13.9 kilometres north of Grand Forks. The lens outcrops on the road west of the Granby River and continues south-southwest up the mountain side for 3.17 kilometres. Exposed widths vary up to 1000 metres.

The deposit is comprised mostly of dark bluish grey to light grey, fine grained, thin bedded limestone containing chert nodules. The limestone is cut buy numerous white calcite stringers and frequently intruded by dykes. Near the dykes the rock is recrystallized to medium grained marble. Some discontinuous layers and lenses of volcanics are present within the limestone. A sample of chips taken randomly along 213 metres of limestone in a road cut on the north end of the lens contained 48.76 per cent CaO, 0.88 per cent MgO, 10.16 per cent insolubles, 0.62 per cent R2O3, 0.56 per cent Fe2O3, 0.05 per cent MnO, 0.14 per cent P2O5, 0.04 per cent sulphur and 39.41 per cent ignition loss (Minister of Mines Annual Report 1960, p. 143, Sample 9).

A small quarry is situated west of the road, 180 metres south of Lime Creek at an elevation of 698 metres. The quarry was operated sometime earlier this century as a source of marble.