Not far from the tech campuses that have minted billionaires, residents in Silicon Valley have lost patience with homeless encampments that have sprouted along bike paths and parks in San Jose.

Mattresses, plastic bags and grocery carts have fallen into ravines and choked creeks whose shaded banks once drew hikers, cyclists and kayakers. San Jose closed an entire city park because hundreds of people posed a safety risk by living there permanently in recreational vehicles.

Homelessness along Skid Row in Los Angeles and in the Tenderloin in San Francisco has long defined the problem in California, but the most intense battles this year over encampments have emerged elsewhere in the state. Local leaders have vowed to take more aggressive steps, making use of a Supreme Court decision last year that empowered them to penalize people for sleeping on the street.

In San Jose, Mayor Matt Mahan, a Democrat, recently called for arresting homeless people if they refused shelter three times.

It’s rare for leaders in the liberal Bay Area to adopt such an approach, which critics say criminalizes homelessness. But his idea has drawn widespread support. While there remains opposition, interviews with residents, elected officials and advocates show that rising frustration with homelessness is making Silicon Valley voters desperate for action and leading them to proposals that once would have seemed too right-leaning for these heavily blue cities.

“We can have progressive goals, but we have to have pragmatic ways of achieving them,” Mahan said in an interview with the New York Times.

San Jose is the largest city in Northern California, with nearly one million residents, but it has long been overshadowed culturally and politically by San Francisco. Most of its population lives in suburban neighborhoods that are only slightly more affordable than the wealthy Silicon Valley enclaves north of the city.

Approximately 6,000 people in San Jose live in shelters, on the streets, along riverbanks and in vehicles. Homelessness is the top concern among San Jose residents by a two-to-one margin, according to city surveys.

Mahan, a 42-year-old moderate Democrat and tech entrepreneur who has been mayor since 2023, tapped into that anger and decried a crisis of homelessness, crime and dirty streets in San Jose the first time he campaigned for the city’s top job. He vowed to bring a “revolution of common sense.”

The goal of his new plan, he said, is to invest heavily in building more shelters in San Jose and to move homeless people who refuse housing into mental health treatment to help them onto a better path. But it is possible that those living on the streets could serve jail time.

“Homelessness can’t be a choice,” Mahan said. “Government has a responsibility to build shelter, and our homeless neighbors have a responsibility to use it.”

His proposal has drawn ire from advocates for homeless people, who have said that it ignores the root cause of homelessness: the high cost of living in San Jose and other California cities. But the San Jose City Council has given its initial approval, and a final vote is scheduled for June.

The appetite for such policies seems particularly high in Silicon Valley and adjacent communities at the moment. Last month, the nearby city of Fremont banned homeless encampments altogether and initially tried to penalize anyone who provided relief supplies to homeless people. (The City Council rescinded that provision after drawing intense criticism.)

The Bay Area has long had progressive ideals, including a tolerance for people living on the streets. But voters lately have gravitated toward candidates who have promised to address quality-of-life concerns such as crime and clean streets. That was the case last year in the San Francisco mayoral contest and seems to have had an effect on the mayor’s race in Oakland this month.

San Jose and Silicon Valley have been ahead of the curve in that regard.

Ro Khanna, a progressive Democratic congressman whose district includes parts of San Jose and Fremont, said that his constituents had long prioritized public safety and that the area had tended to attract residents drawn by quieter suburban neighborhoods.

“I arguably represent the safest district in California, if not the country,” Mr. Khanna said. “This is one of the main reasons people live there — they want the safety.”

Justin Imamura, 42, started a nonprofit in San Jose to clean up creeks after noticing how much trash had accumulated in the city, largely from sprawling encampments. The riverside bike paths he grew up riding on are now largely inaccessible because of tents and waste, including discarded needles.

“I don’t feel comfortable sending my kids on a bike ride down there by themselves,” he said. “I want my kids to be able to experience what I experienced growing up — it’s definitely a bummer.”

In a San Jose shopping plaza with brick storefronts and rows of manicured palm trees, Tesla drivers scrolled through their phones or napped in their leather seats while they charged their vehicles on a recent afternoon. Directly across the street, dozens of tents were perched on the banks of the Guadalupe River, where charity workers handed out peanut butter and jelly sandwiches to homeless campers.

Raoul Mahone, 60, sat on a wooden pallet in front of the green tent where he sleeps each night. He nodded to the pinkish-purple blooms of the redbud tree under which he sought shade and the river behind him. Nothing, he said, could persuade him to go indoors.

“They take away paradise and put you in a shelter,” Mahone said. “They want to lock up the homeless people.”

In 2024, roughly 187,000 people were homeless in California, the highest figure ever recorded in the state, according to an analysis by the Public Policy Institute of California. Though California doesn’t have the highest per capita rate of homelessness in the nation — that would be in Hawaii and New York — the problem is more visible here because of how many homeless people are unsheltered.

While California is home to a quarter of the nation’s homeless population, it is home to half of its unsheltered homeless population. The state lacks enough housing, and its weather is more forgiving for those who try to live on the street, in tents or in cars.

Mahan has promised to build more than 1,000 new temporary housing units — mostly converted motel rooms — by the end of 2025, which would double the city’s shelter capacity. But he wants an accompanying ban on camping near the new shelters and wants to give the city attorney the power to charge anyone who refuses shelter more than three times in 18 months with misdemeanor trespassing. Mahan said the camping ban was necessary to persuade San Jose residents to allow shelters to be built in their neighborhoods.

“There has to be some accountability for coming indoors,” he said. “The failure to do that is going to be a disaster.”

Nationwide, 150 cities, roughly a third of them in California, have imposed new restrictions on homeless encampments since the Supreme Court decided last year to allow state and local governments to prohibit outdoor sleeping, said Jesse Rabinowitz, a spokesman for the National Homelessness Law Center in Washington.

Focusing on temporary shelter and issuing tickets for violations, as San Jose is doing, ignores the reality that homelessness increases as rents rise, he said.

“We’re never going to jail or arrest or ticket our way out of homelessness,” Rabinowitz said. “It’s not a criminal, legal issue. It’s an economic issue.”

Other detractors have said Mahan simply wants to clean up San Jose before the Super Bowl and the World Cup come to the region next year. And some residents find Mahan’s proposal futile.

Efren Ibarreta, 60, an avid hiker who lives in San Jose, began volunteering to lead cleanup efforts near San Jose’s creeks after seeing the amount of trash left behind by encampments. He said he worried that arresting homeless people could be self-defeating if it ultimately made it harder for them to gain employment and turn their lives around.

On April 16, the San Jose City Council debated a proposal to disband the city’s largest encampment later this year, despite not having enough shelter beds for the hundreds of people who would be displaced. A collection of R.V.s and cars in Columbus Park has long prevented the public from getting access to the city park’s basketball courts, baseball fields and other recreational facilities while trash accumulates there.

Members of the public as well as some members of the City Council expressed concern about clearing the park with nowhere for its residents to go. Mahan argued it was more urgent to restore the public’s access to parks and trails, even if there aren’t yet enough available beds.

“If we hold ourselves to an impossible standard that no other city in our county holds itself to, then we’ll be left with the status quo,” he said.

The City Council unanimously approved the plan to clear the park.

Soumya Karlamangla is a New York Times reporter who covers California.