Lake No. 3 is in the same general depression that contains Ironmask Lake (092INE073) and Polygon Lake (092INE074) and is separated from the latter by a divide about 12 metres high. Altered volcanic agglomerate of the Upper Triassic Nicola Group is exposed along the shoreline at the east end of the lake; diorite of the Cherry Creek unit of the Late Triassic-Early Jurassic Iron Mask batholith outcrops on the hill to the south.

The lake was completely dry when examined in October 1937. The surface carried a heavy encrustation of dried salts over an area of 1.6 hectares beneath which was soft sticky mud. The nature of this mud restricted drilling to a zone close to the shoreline. Two 1.5-metre holes, one at each end of the lake, intersected gravelly mud at 1.2 metres; no crystals were found. It is understood, however, that drilling by local parties in the past disclosed a permanent crystal bed beneath 1.5 metres of mud. Neither its thickness nor extent were determined. An analysis of a sample of the white surface crust yielded 48.6 per cent Na2SO4, 19.8 per cent MgSO4, 1.9 per cent Na2CO3, 2.5 per cent MgCO3, 2.7 per cent CaCO3 and 21.6 insoluble (Bulletin 4). It is assumed the sodium sulphate mineral is mirabilite and the magnesium sulphate mineral, epsomite.