From this Al Jazerra story that we found at IPS, Rob Reynolds reporter interviewed a couple who lives in one such city.
They call it Tortilla Flats - a haphazard cluster of tents and tarps sprawling across a sidewalk and a vacant lot smack in the middle of Fresno, a city of 500,000 in California's Central Valley.
The tent city, reminiscent of the Depression-era "Hoovervilles" depicted by author John Steinbeck in his classic novel "The Grapes of Wrath", is home to a shifting population of about 70 homeless people.
That's where I met a couple named Kerry and John. They asked me not to use their last names. They live in a cramped two-person tent strewn with blankets and clothes. Both are native to the Valley. And both are now homeless for the first time in their lives.
Kerry was a preschool teacher until a year ago, when her world caved in. "I got sick," she told me. "Ulcerative colitis. Ended up losing my job, and ended up here. Ran out of health insurance and money and this is what happened."
John, a shy young man who used to work as a barber, told a rambling story about bad breaks, crooked employers and jobs that didn't pan out. Now he passes the time playing with two pigeons he rescued and tamed as pets.
"Gets to the point where time does not mean much anymore," he said. "Time is just time. We're just waiting for the big break - a chance to rebuild our lives."
Homeless camps like this one have formed in several places around California. People here have formed a kind of community, complete with a "town council" of elders who meet nightly.
Many of those living in the camps are chronically homeless men with mental health issues or drug and alcohol problems. But many others are former members of the working or middle classes who have fallen off the economic ladder.
"It's a real shock when you come down here," Kerry said. "You don't know whether people will befriend you or not. People have, luckily. But there are a lot of dangers out here - everywhere you look. Especially at night."