Siwash Creek flows north and west from Spider Peak into the Fraser River at a point three kilometres northeast of Yale. Numerous gold occurrences are located within its drainage basin.

The lower stretches of the creek are underlain by metamorphic rocks assigned to the Cretaceous and/or Tertiary Custer Gneiss in fault contact with Permian to Jurassic Hozameen Complex sediments to the east. Up stream, members of the Hozameen Complex are in fault contact with Early and Middle Jurassic Ladner Group sediments. This contact, the Hozameen fault, is a major, steeply dipping, north-northwest trending fracture system extending from northern Washington State to the Fraser River. Most of the mineral occurrences in the area lie east of but generally close to this fault, which encloses metaplutonic rocks of the Coquihalla serpentine belt between Mount Dewdney and Siwash Creek. The Ladner Group and, to a lesser extent, Hozameen Complex rocks are cut by a variety of small intrusive bodies of unknown age, ranging in composition from gabbro through granodiorite to syenite. The gold occurrences appear to be genetically related to these intrusions.

Numerous unsuccessful attempts have been made to mine the bedrock gravels of Siwash Creek by means of shafts, adits and sluicing operations. These include efforts by the Pacific Northwest Corporation around the turn of the century, the Siwash Creek Hydraulic Company between 1911 and 1915 and the Azalea Mining Company in 1925 and 1926. The gravels were also tested, in 1950, by Canadian American Mines Incorporated. Most of the gold recovered is said to have been found in gravels "which overlay a layer of clay". Total recorded production for the creek is estimated to be 529 grams (Bulletin 28, page 42).