Too many rules and black-market rivals could stifle California’s marijuana industry, experts say

LAS VEGAS—Nearly 20,000 people, eager to profit as cannabis becomes legal in more places around the world, learned last week that tapping one of the biggest markets, California, will prove challenging because of the state’s legendary regulations and huge black market. Investors, growers, regulators and others gathered for the country’s biggest marijuana business conference, MJBizCon, held…