The Mastodon showing is located east of Hastings Arm approximately 19 kilometres north of Anyox on Observatory Inlet. It has been evaluated in the past for gold and silver mineralization.

The showing consists of a siliceous replacement zone 0.3 to 1.8 metres wide in a 30 to 60 metre wide belt of Middle-Upper Jurassic Hazelton Group metasedimentary rocks within granitic rocks of the Eocene Coast Plutonic Complex. This zone trends northwest for 820 metres between elevations of 120 and 260 metres on the north side of Granite Creek. The zone consists of erratic veins, veinlets, patches and blebs of quartz mineralized in places with pyrite, and less frequently with sphalerite and minor galena. Mineralization is best developed in the central part of the zone at an elevation of 180 metres. Trenching and stripping revealed that this zone continues across Granite Creek to the southeast.

Precious metal assays range from trace gold and silver over 1.5 metres to 11.0 grams per tonne gold and 3.4 grams per tonne silver over 0.46 metre (Minister of Mines Annual Report 1934, page B13).

Initial documented work in the showing area was conducted prior to 1934 and consisted of prospecting, excavation of 22 hand trenches, driving two short adits and bedrock sampling. There is no record of further work subsequent to 1934, probably due to some confusion with respect to the precise location of the property. The Mast claims were located in February 1994 and limited work in September 1994 included an attempt to locate the original trail leading from the mouth of Granite Creek to the 1930s workings, prospecting and the collection and analysis of one bedrock sample. No work was carried out between 1995 and 1997. In 1998, prospecting and bedrock sampling was conducted.