To stay energized — and sane — the farm’s trimmers maintain a steady diet of yerba mate tea, music, podcasts and audiobooks, including all 12 hours of J.R.R. Tolkien’s “The Silmarillion” and the entire canon of Terence McKenna, the American philosopher who advocated the use of psychedelics plants.

And for those wondering: No, they don’t get high on the job. “I’m not a productive stoner,” Mr. Kuehl said.

Some trimmers grumble about “cherry pickers,” who select the largest cannabis buds for themselves, leaving the others with smaller specimens that won’t amount to as much weight. And don’t even think about blasting heavy metal. “You want to keep spirits high,” Mr. Kuehl said. “Otherwise you can have drama pretty quick if you’re trimming for 12 hours a day.”

The combination of marijuana and close quarters has occasionally burst into violence. Seven trimmers were charged with taking part in the brutal murder and robbery of a Mendocino cannabis farmer in 2016. In June, a New Hampshire man was found guilty of beating a fellow itinerant laborer to death at a Covelo marijuana farm, after a disagreement about the victim’s dog.

In many ways, Covelo is the Wild West of weed. The town is an hour and a half from the nearest police station. Marijuana groves are pretty much everywhere, in greenhouses concealed within tall wood walls and hidden behind sheets of black tarp on homesteads nestled in the surrounding hills. Yet one black market pot grower, who asked not to be identified to avoid arrest, said an undercurrent of paranoia ran through the town’s main industry, in part because of the fear of getting robbed. “I have cameras and security alarms, but when you’re out in the middle of nowhere, who you going to call?” he said. “This place is kind of lawless.”

If there is one concern that unites growers, trimmers and law enforcement agencies, it is Mexican drug cartels. In recent years, the criminal groups have illegally cultivated millions of marijuana plants on public and private lands in the region. To sustain the illicit operations, the authorities say the heavily armed cartels often steal water from rivers and streams, and poison the environment with toxic fertilizers and pesticides while leaving behind hundreds of thousands of pounds of trash. The authorities have spent millions of dollars trying to eradicate the cartel operations, which continue to plague the area and its residents.

But trimmers say they have more to worry about than cartels.

Nicole Tamaura, 23, a Mexican-American from Tijuana who started trimming five years ago, the last three in Covelo, has her share of horror stories. As she smoked a fat joint outside the library one afternoon, Ms. Tamaura recounted stories of unscrupulous growers she said refused to pay her, of a police officer who she said held a gun to her head, and of frequent sexual harassment, an ordeal made worse by the remote nature of the work. “When you’re alone out here as a girl it’s really scary,” she said. “I know girls who’ve disappeared.”