Several beds of very pure limestone run through the islands, the most prominent crossing Orcas and the northwest tip of San Juan where a massive ledge rises at Roche Harbor. Troops stationed at nearby English Camp during the joint occupation were the first to make lime, used for many building and manufacturing purposes and a key ingredient of concrete. Over the next 15 years various would-be entrepreneurs, including Lyman Cutlar, attempted to exploit lime deposits at Roche Harbor, on the west coast of San Juan (where Lime Kiln Point State Park is now located), and on Orcas.
Large-scale production at Roche Harbor began in 1886 after Indiana-born lawyer John S. McMillin (1855-1936) acquired a controlling interest in the property. Blessed with a deep bay adjacent to the rich limestone deposits, Roche Harbor grew rapidly, becoming the largest lime works in the west and the leading employer in the county. For 50 years until his death, McMillin ran the plant and the company town that he built around it. As head of the Republican party, he dominated San Juan County politics for decades.