The Horn region is mainly underlain by Upper Triassic volcanic and sediment rock of the Stuhini Group. Syentic Stocks of the Galore Creek Intrusions (Copper Mountain Plutonic Suite) intrude a few kilometres to the southest. Larger plutons of the Early Jurassic Texas Creek Plutonic Suite (monzodioritic to gabbroic) and the Paleocene to Eocene Sloko-Hyder Plutonic Suite (granite) intrude further to the west.

Stuhini rock in the Horn area consists of augite porphyry basalt flows, andesite flows, and breccia and calcareous tuff. Latite porphyry and felsite dikes from 3 to 6 metres wide cut these rocks. One of the latite dikes is traced to a tongue of syenite of the Galore Creek Syenite Complex. Augite porphyry basalt and basalts contain traces of chalcopyrite in fractures. Spotty malachite is also observed.

During the 1965 field season, a geologic mapplng program was carried out by Silver Standard Mines Ltd., a part owner of the Racicot Syndicate.