On Monday, California, the US’s most populous state, and the world’s sixth biggest economy, will officially legalising cannabis. Overnight a shadow industry worth billions of dollars annually will emerge into the light, taking its place alongside agriculture, pharmaceuticals, aerospace and other sectors that are regulated and taxed. It will answer to the newly created Bureau of Cannabis Control. California legalised pot for medicinal purposes in 1996, ushering in a web of dispensaries, spin-off businesses and creeping mainstream acceptance. That culminated in voters last year approving proposition 64, a ballot initiative which legalised pot sales for recreation. History will mark the date it came into effect: 1 January 2018.