A quarry was developed on the coast of Mayne Island in sandstone of the Upper Cretaceous Nanaimo Group, Gabriola Formation. The sandstone is light to medium brown in colour, has a fresh uniform texture and is medium-grained (0.06 to 2 millimetres). Beds strike east and dip north at 10 degrees. The quarry is 34 metres long by 3 to 4 metres high and was developed along joints striking northwest and dipping steeply southwest. Vertical cross joints strike northeast and are spaced between 1 and 5 metres apart.

Mayne Island sandstone was used (in part) to construct Postal Station C in Vancouver, at the corner of Main and 15th streets. Potential reserves of sandstone are exposed for at least 100 metres along the coast east and west of the quarry. No production figures are available.