The Red Cliff Extension showing is located on the north side of Lydden Creek about 2.4 kilometres northwest of the confluence with the Bear River, 19 kilometres north of Stewart.
The area is underlain predominantly by andesitic tuffs and flows of the Lower Jurassic Unuk River Formation (Hazelton Group) (Bulletin 58; 63). The volcanics are cut by an east trending zone of fracturing.
A 3.6 metre wide zone of silicification is exposed at an upper opencut. The zone, comprising quartz, jasper and calcite, contains pyrite, minor galena and chalcopyrite. A lens of chalcopyrite-rich material is exposed in the lower opencut.
The Red Cliff Extension claims (the Red Cliff Extension, Copper Hill 1 and Combination Fr. claims) were staked before 1909. That year the Red Cliff Extension Mining Company Limited was formed and acquired the property. Work by the company included one 24 metre long adit and several opencuts.