The Sombrio River flows south, off of San Juan Ridge, into the Strait of Juan de Fuca.

The area is underlain by metamorphic rock (slaty schists) of the Jurassic to Cretaceous Leech River Complex. Basalts and basaltic pillow lavas of the Eocene Metchosin Volcanics are exposed to the south. The Leech River Fault separates these and stretches from west of Victoria westward along the Leech River and Loss Creek valleys, reaching the coast near Sombrio Point.

Placer gold occurs almost exclusively in the gravels of the streams that drain the area that is underlain by the slaty schists of the Jurassic to Cretaceous Leech River Complex (Formation). Fairly coarse gold may be found in the gravels of virtually all these streams. The gold in recent gravel deposits is likely derived from the numerous quartz veins that occur in the slaty schists. These veins are seldom more than small stringers and lenses a few centimetres wide and approximately 1 metre in length. The only metallic minerals in the veins are a little pyrite or chalcopyrite and free gold. The veins are generally too small and too barren to be profitably mined.

Bulletin 21, from 1946, states that placer miners have worked the following rivers and streams of Vancouver Island: China and Loss creeks, and Leech, Gordon, Jordan, Sooke, Sombrio, San Juan, Bedwell, Nanaimo, Gold, and Zeballos rivers.

It appears that most of the gold is derived from bars or in crevices in the bedrock of the river bed, or from benches along the side of the river. Small, clear- pink to deep- red garnets are also reported.

The Spaniards first identified gold in the area in 1792 (see Sombrio Point Placers, MINFILE 092C  044). The placer deposits were re-discovered in the late 1800’s in association with placer gold exploration on the island, following the discovery of the Leech River Placers (MINFILE 092B  078) in the 1860’s. Minor work by local prospectors has continued through to present. The lower part of the Sombrio River is located in Juan De Fuca Provincial Park.

In 2008, Le Baron prospected the area as the Sally claim. In 2011, the area was prospected as the Shada-Lee claim.