Undocumented workers are also plagued by low wages, which aren't keeping pace with the rising costs of housing. In Fresno, fair market rents went up 52 percent between 2000 and 2008, according to the National Low Income Housing Coalition. Now, the typical two-bedroom apartment costs $805 a month, far out of the reach of workers like 21-year-old Juan Garcia, who came from Mexico.

This hardship has only been exacerbated by disappearing jobs in the Central Valley, where an ongoing drought is turning some of the world's most fertile farmland into a desert. This year, the region's water districts are expecting deep cuts to water deliveries –– anywhere from 85 to 100 percent. Job losses could total 95,000 statewide, resulting in up to $2.8 billion in lost income, according to Richard Howitt, an agricultural economist at the University of California, Davis.

That has left workers like Garcia suspended between two countries. In neither country is there a guarantee of a livelihood, and home is all too often an abstraction. At least in Garcia's native state of Colima, there are always the comforts of family.

"It's better in Mexico," Garcia said. "I'm going back."

In Fresno and other struggling cities, which perpetually strive to boost tax revenues with development, tent cities are often seen as symbols of criminality and dereliction, glaring setbacks to neighborhood revitalization efforts. That perception is common wherever informal urbanism exists, said Mehrotra, and it often leaves squatter camps on the brink of ruin.

"You are always on the edge of demolition," Mehrotra said. "There's a kind of insecurity in the lack of tenure on the land."

This hit home in Fresno a few years ago, when workers began raiding encampments throughout the city, tearing down makeshift homes and destroying personal property in the process. The city of Fresno and the California Department of Transportation conducted these sweeps in the name of public health, citing citizen complaints about open-air defecation.

Yet the raids did nothing to stop tent cities from forming, and they ultimately led to lawsuits. In October 2006, residents who lost their homes in the raids filed a class-action suit against the city of Fresno and the state of California. A U.S. district judge ordered the defendants to pay $2.3 million in damages.

Hundreds of miles to the south of Fresno, there's also been a battle over tent cities in the Inland Empire, an industrial stronghold that stretches out into the deserts east of Los Angeles. Flying into Ontario International Airport, one can see the nucleus of this struggle, in a neighborhood less than a mile from the tarmac.

There, on a stretch of vacant land surrounded by aging homes and abandoned orchards, tents are arranged in neat rows oddly reminiscent of the region's grid of warehouses, rail yards and sprawling truck lots.

This used to be one of Southern California's largest squatter settlements, an unruly village of tarp and scrap wood that grew until some 400 residents called it home. People moved here from as far away as Florida, recalls Brent Schultz, Ontario's Housing and Neighborhood Revitalization Director.

Schultz said local officials would rather see Ontario as an economic engine, and they were disturbed to find out that it was becoming a magnet for the dispossessed.

"We're not," Schultz said, "going to be a repository for a region's homeless."

Rather than simply bulldoze the makeshift neighborhood, Ontario officials embarked on a $3 million campaign to discipline and punish squatters, setting up a formal camp where tarp dwellings became symbols of order.

In the spring of last year, police and code enforcement officers issued color-coded bracelets to distinguish Ontario residents from newcomers, then gradually banished the out-of-towners. Then they demolished the shanties and set up an official camp with a chain-link fence and guard shack. Residents were issued special I.D.s and a strict set of rules: No coming and going after 10 p.m., no pets, no children or visitors, no drugs and no alcohol.

About 120 people stuck around, but many left to escape the regimentation. As of late January, the population was less than 50.

"It's like a prison," said Melody Woolsey, 40, who has lived in both versions of the encampment.