The fake fishing pond, which looks like a moat, is her pride and joy and the source of her income. She devotes hours to furnishing the game with prizes meant to entice young customers. The 44-year-old says she will pay no attention, however, to the census questionnaires that millions of Americans -- most of them stationary, settled Americans -- are filling out this month.
"I'm a lost soul. I haven't been on the records for 14 years," said Obrentz, who lives in a closet-sized RV cabin that lands in a new town each week. "I think we're all pretty much lost souls here."
Carnival and circus workers have populated the American landscape at least since President George Washington visited the nation's first circus in 1793. Census workers have been counting the nation's people every decade since 1790. So for at least 200 years, they have faced the special challenge of trying to keep track of a fluctuating population of nomadic entertainers.
Obrentz uprooted herself from mainstream society at 16 when she ran away from her San Jose home over Easter weekend. Back when the labor rules were not so strictly enforced, she would sleep peacefully beneath the carnival rides. Decades later, she still waxes romantic about life on the road but also considers herself a professional.
"It's just like a regular job, except we move," she said.
The toughest part of carnival work happens on the first day in a new town, when the brute strength of a caravan of workers transforms a parking lot or an empty field into a wonderland in a matter of hours. The second toughest is the end, when the wonderland reverts to a parking lot in the middle of the night.
At the Butler Amusements carnival that stopped in Antioch's Somersville Towne Center this week, at least half of the ride jockeys -- the workers who set up, operate and take down the rides -- hail from Tlapacoyan, a town in the eastern Mexican state of Veracruz. None of them are sure if they, too, should be counted in the census.
One of them, Clemente Pena, 46, has been working eight years for Butler Amusements, which claims to be the biggest carnival company in the Western United States.
"Some people like sports," he said in Spanish. "I like to travel, so that's why I joined the carnival. I get to know a lot of places, a lot of people."
Pena talks as he crouches beneath a long trailer parked at the Contra Costa County Fairgrounds that is home for him a dozen other Mexican men.
There are two stoves in the hollow beneath the trailer, and he is using one of them to cook a sopa de coditos, a soup filled with pasta and vegetables he bought at a Mexican market in downtown Antioch. Night is falling, and frogs croaking in a nearby creek, as other men set up chairs and a television. Mexico's soccer team is about to play North Korea, beating them 2-1. It is also St. Patrick's Day, and many of the other carnival workers -- the native-born ones, who call themselves carnies -- have gone out to drink at local bars.
The bunks in the trailer above Pena are stacked vertically -- three beds one on top of the other -- though not all are occupied. To explain how he copes with such a cramped lifestyle, Pena recites a proverb: "Todo cabe en un jarrito sabiéndolo acomodar." Everything can fit in a little jar if you know how to accommodate it.
"You have to have an adventurous spirit," he said. "After eight years, you adapt."
When his wife died in an accident eight years ago, the grieving widower was looking for an escape. He applied to be a temporary seasonal worker in the United States, obtaining an H-2B visa that allows him to work for the carnival from February through October. At the end of the season, he goes back home to Veracruz, visiting the son he left in the care of his mother. When they talk on the phone, there are sometimes awkward pauses halting conversation between the boy, now 12, and his dad. The son wants his dad home, but respects what the father is doing for the family, Pena said.
Walking through a Target store in Antioch this week, Pena saw volunteers talking in Spanish to local Latinos about the importance of the 2010 census. They approached him, but he thought it did not concern him. Census officials say it does matter.
"If they are tourists, they're passing through" and are not counted, said Sonny Le, spokesman for the Census Bureau. "But if they're working here, however temporary, they're using services. Even the circus, it uses up the municipal sewer system, the water system, electricity. That's the rationale."
Le said the agency has a plan for counting carnival workers and others who spend their time moving from one place to another. If there is no residence where they live and sleep most of the time, they are counted "where they live and sleep more than anywhere else," census documents say. If there is no such place, they should be counted as living wherever they are on April 1, the official day of the census.
"It's a constitutional mandate," Le said. "The requirement is we need to count everyone. I understand that carnivals and circuses kind of seem trivial, but we cannot leave anybody out."
Census workers will descend later this month upon dozens of encampments, RV parks, bridges and benches looking for people who live outside or in tents and other mobile lodging. In California, the priority will be on the state's tens of thousands of homeless people, not a few hundred carnival workers, but everyone matters in determining the state's true population, Le said.
"We've got our own little city, our own little traveling city on wheels," said Laddy Buck, 21, who joined the carnival when he lost a job at a Quiznos in Stockton. "I don't worry about mail or anything like that."
Fellow carnival worker Marilyn Souza said she will probably be counted where her daughter lives, in Turlock, where unemployment has reached above 14 percent. The 50-year-old Souza joined the carnival once her children were grown, and she will stick to the road this year until she raises enough money to fix her 1980 Chevy Silverado.
Unlike the Mexican guest workers, who are guaranteed a salary through the rules of the guest worker program, Souza's income depends on the popularity of her games. A rainy day is a lost day.
"I work on commission, so the hurry-up-and-wait is just free time," she said. "If I work for 25 percent, bring in $1,000, $250 is mine. The more we make, the more we make."
Robby Cotter, 38, joined a carnival in Oregon when he was 16, getting the job by telling the boss he was two years older. He has been on the road ever since and passes time by lifting weights. When there is no gym around, or it is too expensive, he makes do with lifting the carnival equipment.
"I used to be in a lot of trouble, in jail a lot. My parents died when I was young," he said. "This job has given me a purpose. It's hard work, but it's an OK life."
As far as he knows, he has never been counted in the census as an adult, and he has no intention of ever participating. In the future, he said, there will be earthquakes and great catastrophe, Jesus Christ will return to Earth and the census will be irrelevant.
"I'm not too into the world. It's a big lie," he said. "I don't believe in the system. It's a big show, a big facade."
Speaking of which, he has a job to do, he said, returning to the parking lot to put up a ride called the Orient Express.