A 1.32 to 3.7 metre thick postglacial deposit of brown to white, jelly-like marl with scattered shells of gastropods and bivalves, occurs on the floor of Cheam Lake on the south side of the Fraser River, 14 kilometres east of Chilliwack. The Cheam Marl deposit lies on 0.6 metre of blue clay which is in turn underlain by sand. The marl has a high organic matter content and is contaminated with mud from inflowing streams. Three samples of marl analysed on a moisture-free basis averaged 43.55 per cent CaO, 0.13 per cent MgO, 9.08 per cent insolubles, 0.61 per cent R2O3, 0.85 per cent Fe2O3, 0.036 per cent MnO, 0.04 per cent P2O5, 0.60 per cent sulphur, 0.48 per cent nitrogen, 4.00 per cent organics and 45.16 per cent ignition loss (Bulletin 40, page 100). A second deposit of marl, up to 4.0 metres thick, underlies 1.6 hectares of land formerly covered by an arm of Cheam Lake to the northeast.

Marl and minor humus was initially pumped from the lake and mined along the east shore by Fraser Valley Chemicals and Popkum Marl Products during the 1940s and 1950s. Cheam Marl Products began strip mining on the northeast corner of the lake in 1949. The lake was eventually drained by the company in 1961 to continue strip mining. Mining operations ceased in 1988. A total of 586,512 tonnes of marl was produced.