Siwash Creek initially flows southwest from Elkhart Lake for 12 kilometres before abruptly turning southeast, continuing for 6.5 kilometres to the mouth of Galena Creek. The creek then flows south for 15 kilometres before entering Hayes Creek, 25.5 kilometres northeast of Princeton.

Most of the creek runs through a steep, narrow, occasionally flat-bottomed valley. The uppermost 5 kilometres of the creek flows through a wide, gently-sloped valley, immediately south of Elkhart Lake.

The gold-bearing placer deposits of Siwash Creek tend to occur in the creek bed and in benches and terraces adjacent to the creek that may represent old-channel remnants. The gravels comprising these deposits appear to be of glacial origin. The coarse gold found in these gravels is rough-edged and erratic in distribution.

Production of placer gold has occurred intermittently along the creek since the early 1900s. Most of this production has been confined to benches above the creek bed. One operation worked by L.J. Cole and T.C. McAlpine in 1933, was located about 11 kilometres above the creek's mouth. This hydraulic operation was situated atop a bench 3 metres above the creek, on its west side, and is reported to have recovered 3.5 grams of gold per cubic metre (Minister of Mines Annual Report 1933, page 175). Colours of gold are reported to have been observed in numerous cuts and pits excavated farther north, between Tepee and Galena creeks.