The Fir Ridge (Rose Lake) showing is located on a small ridge north of Rose Lake.

The area occurs at the boundary of the Cache Creek and Quesnellia terranes and is underlain by the Mississippian to Triassic Cache Creek Group. It is likely that in the area of the showing the rocks are Permian (based on the presence of fusiu-linid foraminifera found in similar lithologies to the south). The contact between the Cache Creek Group and Quesnellia is probably a fault, although nowhere is this contact exposed in the map sheet.

Locally, the area is underlain by chert, argillite, greenstone and limestone. Chalcopyrite mineralization is reported to occur within limestone. Malachite mineralization is also reported in a small outcrop 150 metres to the north.

During 1969 through 1971, Grandeur Resources completed programs of prospecting, soil sampling and a ground magnetometer survey on the area as the Fir Ridge claims, Rose Lake property. In 2010, the area was prospected and geologically mapped as the Onucki Copper claim.