Immediately to the north of Merritt, Middle Eocene Coldwater Formation beds (Princeton Group) overlie Upper Triassic Nicola Group volcanic, volcaniclastic and sedimentary rocks. The sediments consist of arkosic sandstone, conglomerate, shale and local coal seams. On the benches of the hills, gypsum occurs as irregular patches exposed by erosion. Pockets vary in thickness up to 3 metres. Calcite, sand and vegetable matter control the purity of the gypsum. Shipments of 454 tonnes were reported in 1911 after which trenches and pits become filled with debris.