The Similkameen River flows northward for 60 kilometres from the Cascade Mountains to Princeton, where it abruptly changes course and continues southeast for 83 kilometres before crossing into the United States.

The lower part of the river, between Princeton and Hedley, flows in a broad valley flanked on either side by gravel terraces comprised of reworked glacial material. The upper part of the river runs through a wide valley between Princeton and Whipsaw Creek, containing deep gravels in most places. Farther upstream, this valley gives way to a steep canyon that continues to the Pasayten River.

Placer deposits have been worked at intervals for some 48 kilometres along the river. Most recorded production and exploration has occurred along a stretch extending upstream from Princeton for 14 kilometres and continuing downstream past Princeton for 8 kilometres.

The alluvial gravels worked along the river yielded black sands containing fine platinum, in addition to gold. The ratio of gold to platinum recovered from these gravels is 4:1 (Geological Survey of Canada Memoir 243, page 59). Gold is reported to occur as "coarse scales", mixed with a considerable proportion of platinum in similar- sized particles, at one point 5.5 kilometres above Princeton (Geological Survey of Canada Report of Progress 1877-1878, page 156B). One of the larger gold nuggets found on the river weighed 160 grams (Minister of Mines Annual Report 1885, page 495). Precious metals in the gravels below Princeton occur in local, patchy concentrations, making them largely uneconomic for the early placer miners. One of the richer deposits occurred in an elevated bench at Princeton, and consisted of 1.5 to 1.8 metres of cemented gravel on a sand bed. Gravels tested on a bench 5 metres above the river, just below Princeton, averaged 1.83 grams of gold and 0.12 gram of platinum per cubic metre (Geological Survey of Canada Economic Geology Report No. 13, page 94). Farther downstream, a hole drilled to 9 metres depth averaged 1.43 grams per cubic metre of gold equivalent for combined gold and platinum (Western Miner, November, 1948). Several shafts, 1.8 to 2.7 metres deep, sunk on a gravel bench near Bromley Creek, gave "colours" of gold and platinum. Higher values were found at bedrock in this bench (Minister of Mines Annual Report 1926, page 233).

Gold was first discovered on the Similkameen River below Princeton in 1853. The river was extensively worked, largely by individual placer miners, over a 40-kilometre stretch, between 1860 and 1900. One operation in particular, 6.5 kilometres upstream from Princeton, mined 600 cubic metres of gravel in 1895, containing 1.2 grams of gold per cubic metre and a considerable amount of platinum (Minister of Mines Annual Report 1895, page 708). Since 1900, only minor production has been recorded, largely from dredging operations in the vicinity of Princeton. One dredge operated by A.R. Watkins and Sons, 3 kilometres south of Princeton, produced 1400 grams of gold over a two month period in 1941 (Minister of Mines Annual Report 1949, page 228). Shortly afterwards, Cam Roy Mining produced 4320 grams of gold and 824 grams of platinum from about 6000 cubic metres of gravel at the same location in 1941 (Minister of Mines Annual Report 1949, page 228). Atkinson Dredging Company Ltd. also operated a dragline dredge on the Similkameen River between 1947 and 1950. The dredge first mined a 1.6-kilometre stretch, 1.5 kilometres south of Princeton, during 1947 and 1948. Subsequent dredging was conducted on a section beginning 300 metres east of the confluence with the Tulameen River and continuing east for 5 kilometres, between 1948 and 1950. This operation recovered 50,045 grams of gold, 6221 grams of silver and 10,637 grams of platinum from 433,932 cubic metres in 1948 and 1949 (Minister of Mines Annual Report 1949, page 229). No production has been recorded since the ceasing of dredging operations in 1950. Total gold production between 1885 and 1950 is estimated at 229,200 grams. Recorded platinum and silver production is 14,900 and 6200 grams respectively.

Only minor prospecting has occurred since the 1950's. Some exploration work was conducted just south of Princeton and near the mouth of Whipsaw Creek between 1958 and 1969. More recently, gold and platinum were discovered during the early 1980's on the Rosch Ranch, on the east side of the Similkameen River, 7 kilometres south-southwest of Princeton. Work by Kettle River Resources Ltd. and G.F.L. Technologies has outlined a channel, 2 metres below surface, with coarse gold and platinum (Assessment Report 16128, page 5).