The Northwestern Quarries showing is located 1 kilometre southwest of Twin Lakes, 6 kilometres north-northeast of Olalla, British Columbia.

No exploration record prior to 1977 could be found for the Northwestern Quarries area. During 1977 and 1978, Union Oil Co. of Canada Ltd. conducted exploration consisting of induced polarization surveys, scintillometer surveys and limited geological mapping for uranium in the area.

The Northwestern Quarries showing lies along the western margin of a fault-bound basin of Eocene Penticton Group volcanic rocks. At the base of this volcanic succession, lies the Springbrook Formation that consists of massive, unsorted, polymictic conglomerate and breccia with lesser sandstone and tuff. The matrix of the conglomerate and breccia is silty and green. Clasts are dominantly volcanics (45 per cent) and chert (35 per cent) with lesser metamorphic rocks (10 per cent), sediments (5 per cent ) and intrusions (5 per cent). The lowest member of the overlying Marron Formation is the Yellow Lake Member. At the Northwestern Quarries, the Yellow Lake Member consists dominantly of pyroxene-rich mafic phonolite lava with well developed anorthoclase phenocrysts. This is overlain by trachyandesite flows with conspicuous glomerophenocrystic clots of feldspar of the Kitley Lake Member. Highly vesicular, pyroxene-rich basaltic andesite of the Kearns Creek Member overlies the Kitley Lake Member to the east near Twin Lakes. The Olalla rhyolite of the Marama Formation overlies members of the Marron Formation to the immediate north.

Andesite of the Kearns Creek Member of the Marron Formation was reported quarried for dimension stone from the Northwestern Quarries.