UKIAH, Calif.  There is probably no marijuana-friendlier place in the country than here in Mendocino County, where plants can grow more than 15 feet high, medical marijuana clubs adopt stretches of highway, and the sticky, sweet aroma of cannabis fills this city’s streets during the autumn harvest.

Lately, however, residents of Mendocino County, like those in other parts of California, are wondering if the state’s embrace of marijuana for medicinal purposes has gone too far.

Medical marijuana was legalized under state law by California voters in 1996, and since then 11 other states have followed, even though federal law still bans the sale of any marijuana. But some frustrated residents and law enforcement officials say the California law has increasingly and unintentionally provided legal cover for large-scale marijuana growers  and the problems such big-money operations can attract.

“It’s a clear shield for commercial operations,” said Mike Sweeney, 60, a supporter of both medical marijuana and a local ballot measure on June 3 that called for new limits on the drug in Mendocino. “And we don’t want those here.”