Syreeta Lux has a vision for her marijuana plants if voters decide to legalise the drug next week. She could market her product as a premium brand – heirloom strains, raised pesticide-free, each bud cultivated with tender care. She might turn her land, located in woods so dense they block out sight of the nearby Pacific Ocean, into an upmarket tourist spot, like the Napa Valley vineyards. Maybe she'd offer her seeds to science.

"Not only could we be the Napa Valley of marijuana, we could be the Silicon Valley too. We could become a centre for medical research," she said.

Or she could open up her property to families on a day out – bring the children to harvest marijuana instead of strawberries, perhaps. "My dream is to have a pick-your-own farm," she said. "Forget about cleaning, or harvesting. Let people take the green buds and go home. Wouldn't that be fun, the experience of a real marijuana farm?"

They will all be fairly realistic business plans if Californians vote, at the midterm elections on 2 November, in favour of a measure letting anyone 21 or older grow and possess marijuana, and allowing local governments to license and tax retail outlets selling it.

The measure, if it passes, would offer legitimacy to growers who for years have operated in a grey area of the law, and raise a potentially huge new revenue source for recession-hit states.

Calculating the value of a "grey asset" is notoriously difficult, but a recent report estimated California's marijuana crop to be worth about $14bn – seven times greater than the $2bn wine industry. Proponents of the measure say it could raise $1.4bn in taxes.

And, as so often happens in California, its ballot initiative, proposition 19, could set a national model for the control of marijuana use. At least that is the way Lux sees it. "When the Feds finally wake up, the country is going to go the way we are going – like gangbusters."

For the old-time growers, who have been growing cannabis in the remote hills of Humboldt county for decades, a yes vote could sweep away the traces of a renegade existence – though medicinal marijuana was legalised in the 1990s.

However, it could mean economic annihilation. People such as Lux are already losing out to a younger, urban, and more business-savvy generation of growers.

Kevin Jodrey, a well-known grower in the area, said: "It's a 50-50 split. Those that are for it see the possibility of a real future to take marijuana from the dirty backroom where it has been kept all these years and put it forward as a product that has many uses in different capacities, and sell it a fair price. For the other side, it is like, 'how am I going to survive?' The prices are going to plummet. But the reality is it was going to have to change."

Proposition 19 is among nine proposals put before voters this year under California's direct democracy system. Richard Lee, an Oakland businessman, who has been enormously successful in persuading the Oakland authorities not just to legalise pot but to tax it, presented the proposal. His network of indoor cultivation sites and dispensaries pay about $800,000 a year in tax to Oakland city council. When he put up $1.5m to fund the proposition, the Oakland authorities endorsed the ballot measure and approved a plan to build four vast indoor factories capable of harvesting more than 22kg (50lb) of marijuana a day.

But surveys suggest that Californians, after initially embracing the idea of legal marijuana use, are now having second thoughts. A poll by the Public Policy Institute of California found support for the measure falling from 52% last month to 44%, with 49% opposed.

California's governor, Arnold Schwarzenegger, and political candidates oppose the measure, though Edgar Bronfman, a former chief executive of the Seagrams spirits empire, likened the measure to ending prohibition in a newspaper article last week.

However, even opponents of proposition 19 concede that full legalisation and taxation is inevitable.

"Marijuana, for all intents and purposes, is already decriminalised in California. At this point it is the same as a parking ticket," said Roger Salazar, a spokesman for the no campaign. But he added: "While legalisation may be in the offing, this initiative is so flawed, so poorly written, it is just not the way to do it."

California made the first move towards legalising marijuana in 1996 when the state first allowed it to be sold from dispensaries run by co-operatives in a non-profit-making way. Since then, 14 other states and Washington DC have legalised the cultivation and sale of medical marijuana. A Denver alternative weekly, Westword, even has a medical marijuana reviewer. And last month Schwarzenegger lessened the penalty for possession to a $100 fine with no criminal record.

But in the absence of full legalisation it makes for a strange double life. When Lux comes into town, to lobby the local government, as president of the Humboldt Medical Marijuana Advisory Panel, she dresses with triple strands of pearls. Then she returns to the homestead to work in her drying shed, where strands of marijuana with names such as Purple Jesus and Great White Shark are dried out on coathangers.

It is the same across the so-called Emerald Triangle – northern Humboldt, Mendocino and Trinity counties – where marijuana, while still not entirely legal, is a huge prop for the local economy.

Adverts on radio stations promote hydroponic growing systems. Gardening megastores have basil plants in the window but they are invariably stocked with the powerful lights needed to grow marijuana indoors.

At the Humboldt Patient Resource Centre, operating out of a small converted home near Arcata's main street, they see about 100 customers a day turning up with a doctor's note to buy $40 bags of marijuana or edibles: brownies, lozenges, pecan pie. Mary Ellen Jerkovich, the director, has a nutritionist on staff and offers tai-chi and zumba classes at a separate facility. She would like to build the place into a wellness empire, and maybe get tax-exempt status. It is likely the local government would support the venture, she said.

At a meeting last week, the Humboldt county board of supervisors came out in support of proposition 19. "This is our economic future to some extent," Bonnie Neely, a board member said. "We can't ignore that."

But critics argue that the measure would create legal chaos and confrontation with the federal government.

The measure suggests each of California's local authorities develops its own set of rules and tax system on marijuana. It will also elevate marijuana use to a civil rights issue, making it illegal for employers to drug-test employees.

The Obama administration has already stated that it will not tolerate any new moves towards legalisation.

The attorney general, Eric Holder, warned that the federal government would continue to prosecute people who grew and sold marijuana, even if Californians voted for legality. The legal limbo has even established businesses, such as Jerkovich's, worried. "If this one goes through I just see a potential for huge problems," she said. "I personally do not want to deal with any more legal mumbo jumbo."

And it could spell the end for growers such as Lux. In interviews Lee has been scathing of Lux and her contemporaries, describing them as "a bunch of hippies, peace and love, sharing their bud together, like a Coca-Cola commercial".

Now, for Lux, after more than 30 years in Humboldt, living for a long time with no electricity, toilets or phone, and with the prospect of police arrest by raiding parties in helicopters, after raising children and grandchildren and paying her taxes, there is the reality of her back-to-the-land movement having run its course. She is not only stepping into full daylight, but plunging headlong into market capitalism.

"I believe the future for the small farmer is in connoisseur-grade marijuana," said Lux. "Everyone knows there is a difference between a $600 bottle of wine, and a $20 bottle of wine, and a $2 bottle, and that is what we are going to have do to survive – we are going to have to market our quality."