As cash crops go, marijuana is a whopper. The value of California’s 8.6 million-pound pot harvest is about $14 billion, dwarfing wine grapes at about $2 billion, according to state reports. Making it legal, as Proposition 19 on the Nov. 2 ballot proposes to do, presumably would allow banks to lend money, businesses to hire workers and create distribution and retail networks. “There’s definitely a positive economic impact,” said Robert Eyler, Sonoma State University economics department chairman.