Four quarries occur in granodiorite of Jurassic age in the Jurassic to Tertiary Coast Plutonic Complex and are located on Quarry Bay at the southern tip of Nelson Island.

The granodiorite is light grey, uniform and has a medium grained texture. Black blades of biotite and occasional hornblende crystals contrast with the light grey feldspar and quartz matrix. Scattered knots of mafic minerals (less than 1 per cent by volume), up to 3 centimetres wide by 10 centimetres long, are visible in outcrop. Isolated clusters of pyrite are also visible. The largest quarry is 115 metres long and was worked in benches up to 18 metres high.

Spacing between joints and fractures at all four quarries permits removal of large blocks. Greater than 80 per cent of vertical joints and fractures, and over 74 per cent of horizontal joints, are spaced more than 50 centimetres apart. Some 60 per cent of all structures are spaced wider than 100 centimetres. Large reserves remain on site at three of the quarries. Cottages have been built on the site of the smallest quarry. Physical properties are as follows (CANMET Report 452, pp. 85-86):

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            Specific gravity                       2.657
            Crushing strength (dry) (lbs/sq.in.)  34,823
            Transverse strength (lbs/sq.in.)       2,871
            Shearing strength  (lbs/sq.in.)        2,300
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These quarries have been operated intermittently since the mid- 1800's, providing stone for a number of buildings and monuments in Vancouver, Victoria, New Westminster and Nanaimo. The stone has also been exported to Australia, California and Hawaii. Vancouver Granite Company Ltd. operated the quarries more or less continuously during the first half of this century. The stone was marketed under the trade name "Nelson Island Grey". No production figures are available.