Two Lower Permian limestone beds of the Devonian-Permian Chilliwack Group outcrop as two north-trending bands 300 metres apart along the base of Mount Cheam for at least 600 metres, 1.3 kilometres southeast of Popkum on the south side of the Fraser Valley. The western band is at least 24 metres thick while the eastern band is at least 60 metres thick. The limestone and interbedded siliceous argillite strike 150 degrees and dip 30 degrees northeast.
Both bands are generally composed of dark grey, medium-grained limestone containing some chert lenses and beds, and a few veinlets and masses of quartz and calcite. At the north end of the western band, the limestone displays lenses and thin beds of fine grained siliceous limestone. Two chip samples taken in succession across 24.3 metres of strata in a quarry in the western band averaged 45.75 per cent CaO, 0.68 per cent MgO, 15.58 per cent insolubles, 0.205 per cent R2O3, 0.14 per cent Fe2O3, 0.0155 per cent MnO, 0.0888 per cent sulphur and 37.44 per cent ignition loss (Bulletin 40, page 42).
Limestone was produced by various operators (Western Canada Lime Company Limited, Adanac Lime Corporation Limited, Fraser Valley Lime Supplies Ltd.) between 1917 and 1970 from two quarries in the western band. Most of the production came from a quarry on the north end of the band. A smaller quarry lies just to the south. Most of the limestone was quarried for pulverized stone (agricultural purposes) and roofing granuals by Fraser Valley Lime Supplies between 1949 and 1970. Production totalled 113,761 tonnes of limestone; includes some trucked in from other sources. Some production values are from historical fiche.