The Richmix Company mined shale from the Fireclay seam on the southeast slope of Sumas Mountain. The property adjoins the Clayburn Company property (092GSE004). The open pit workings and the under- ground portals are located north and northeast of Kilgard. Until 1950, the room-and-pillar method of underground mining was used. When the seam was worked out to the property boundaries, the company retreated up the slope, pulling pillars. As the surface was reached, underground mining was stopped, the overburden was bulldozed off, and strip mining methods were implemented.

The Fireclay seam and Tertiary shales mined are part of a sedi- mentary sequence that caps Jurassic to Tertiary granitic rocks of the Coast Plutonic Complex on Sumas Mountain. The shales are thought to be part of the Eocene-Oligocene Huntingdon Formation.

The Fireclay seam was deposited in an arc-shaped basin that averages about 500 metres east and west. The seam consists of dark grey, non-calcareous shale. The material is classed as a moderately dense firing refractory clay.

Some of the fireclay was exported raw to the United States and the rest was made into refractories in local plants. No production figures are available.