This location is the modern beach extending from the mouth of the Salmon River north 9 miles to the Hagemeister Island quadrangle boundary. The modern beach is a 75- to 140-m-wide sandy gravel veneer over older unconsolidated deposits. From north to south, the landward margin of the beach is against 4 miles of bluffs to 8 m high of poorly sorted, stratified, pebble and cobble gravel with some thin discontinuous sand lenses; 1.5 miles of talus and bedrock of the Red Mountain ultramafic pluton; and 3.5 miles of bluffs to 16 m high of unconsolidated pebble gravel, clay- and silt-rich deposits with some iron-cemented gravel, and local sand- and peat-bearing sections (Mertie, 1940).

Black sand streaks and lenses are present locally along the beach. These were tested by panning early in the exploration of the area but only traces of platinum were found (Mertie, 1940, p. 36). Systematic sampling and evaluation of the beach sands was later accomplished by Berryhill (1963), Bond (1982), Ulrich (1984), and Fechner (1988). Berryhill (1963) collected auger or shovel samples at 16 locations and Fechner (1988) collected mini-sluice or hydraulic concentrator heavy mineral concentrates at 20 locations. Berryhill (1963) showed that chromite was a major constituent of the heavy mineral concentrates, but that both gold and platinum were commonly present only in trace amounts. One sample collected about 2 miles north of the mouth of Salmon River contained 0.0736 ounce of gold and 0.0573 ounce of platinum per cubic yard. A composite sample of black sands from beaches throughout the Kuskokwim Bay-Chagun Bay area contained 33.8 percent acid-soluble iron, 12.1 percent Cr2O3, and less than 0.02 ounce of Au, Pt, and Ag per ton (Berryhill, 1963, p. 13).

Analytical data reported by Fechner (1988) showed that the beach sands commonly contained detectable Pt and Au. The highest values, 0.26 ounce of PGM per cubic yard and 0.1029 ounce of Au per cubic yard, were from the Flat Cape area between the mouth of Salmon River and Red Mountain. Microprobe analyses of the PGM grains showed that they comprise 0.5 to 4.5 percent Rh, 0.2 to 1 percent Ru, 32 to 89.1 percent Pt, 1.6 to 47.8 percent Ir, 0.8 to 15.9 percent Os, and 3.2 to 8.9 percent Fe; the gold fineness ranged from 548 to 863 (Fechner, 1988, p. 24). Fechner (1988) also collected samples of older unconsolidated materials in the bluffs along the beach and showed that small amounts of Pt and Au are present in these deposits both north and south of Red Mountain. Hessin and others (1978 [OF 78-9-J; OF 78-9-K; OF 78-9-L; OF 78-9-P]) and Coonrad and others (1978) showed that samples of bottom sediments collected offshore of the present beach contained anomalous concentrations of Cr, Co, Ni, Hg, Au, and Pt in several places.