Underlying rocks in the area belong to the Upper Proterozoic Horsethief Creek Group. They consist of calcareous pelitic schists, amphibolites, marbles and quartzites.

Gold occurs in quartz veins around the heads of McCulloch and Graham creeks. These veins are thought to have been the source of the placer gold. The placer gold occurs as coarse grains and nuggets close to the bedrock and as fine colours in the gravels and surface sort. The gold is also angular and slightly porous.