The scoop behind "His Highness" Willie Nelson's business model for pot shoppes -- he expects his product to be available in January. Legal marijuana is the fastest-growing industry in the United States, with 74 percent growth in 2014, according to a recent study by the ArcView Group, a Silicon Valley investment research firm. Last year, it generated $2.7 billion in sales and delivered more than $200 million in tax revenue to the legal states. In Colorado alone, the $88 million raised from pot was more than double that from alcohol.