SALINAS, Calif. (AP) – Farmers in the self-proclaimed “Salad Bowl to the World” started plowing their spinach crops under and laying off workers as government inspectors examined fields and packing houses Tuesday for the source of the deadly E. coli outbreak.

After poring over water quality reports, worker hygiene tests and other food safety measures, the inspectors were unable to pinpoint immediately how the bacteria made it into locally grown bagged spinach, causing one death and sickening more than 100 other people across the country.

And it is increasingly unlikely they will ever zero in on the source, said Robert Brackett, director of the Food and Drug Administration’s Center for Food Safety and Applied Sciences.

FDA investigators visited fields and factories in the Salinas Valley that have been linked to the two companies that recalled spinach products – Natural Selection Foods and River Ranch Fresh Foods.

The teams also inspected other locations, looking for evidence of contaminated runoff; checking for animal droppings in the fields; examining sanitary conditions inside the plants where produce is processed; and taking samples from produce itself. E. coli is commonly spread by human or animal feces.

“They will look for any obvious or even suspected places where this organism could gain access to the produce,” Brackett said.

The absence of any immediate evidence of widespread contamination is good news for the industry, but growers and processors say the scare has already done damage to their products’ reputation, and they are wondering when how long it will take for consumers to feel safe eating spinach again.

At least two lawsuits over youngsters who fell ill have already been filed, in New York and Utah.

“If it stays focused on the spinach, it’s still bad,” said Jim Bogart, president of the Grower-Shipper Association of Central California. “Worse-case scenario, where consumers don’t get the message this doesn’t mean all vegetables are tainted, it would be devastating.”

Spinach was a $325 million industry in the U.S. in 2005, and California produced 74 percent of the nation’s fresh crop and 67 percent of the spinach that gets frozen or canned. The Salinas Valley accounts for roughly three-quarters of the state’s share.

With that market disappearing in a matter of days, some valley farmers were already writing off their spinach crops, plowing the fields under and preparing to plant broccoli, cauliflower and cabbage.

With about a month left in the current growing season, those who invested most heavily in spinach are still hoping the FDA will lift its warning before the last of their leaves are ready to be picked, said Henry Gonzales, Monterey County’s chief deputy agriculture commissioner.

Spinach farmers were also laying off field hands, but most quickly found work picking other crops in what is typically a busy harvest season, said Marc Grossman of the United Farm Workers union.

“The overall effect is not that great because spinach is a relatively small part of growing there,” he said. “Many workers have been able to find work in lettuce and broccoli.”

Depending on how long the spinach warning lasts, related businesses such as seed companies and pesticide sprayers could also take a hit, Gonzales said.

Cool ocean air and morning fog give the Salinas Valley a mild climate that makes it ideal for growing salad vegetables. From the city of Salinas, a shaggy carpet of lettuce and other leafy greens stretches for miles inland, broken occasionally by fields of strawberries, cauliflower, celery, spinach, artichokes and wine grapes.

The area rose to prominence as an agricultural region in the 1920s, when growers started shipping iceberg lettuce in boxcars packed with ice. Cheap labor arrived during the Depression – a westward movement chronicled in the books of former Salinas resident John Steinbeck – as workers fled the Dust Bowl for the Salad Bowl.

The growing popularity of pre-washed salad mixes and spinach over the past two decades has been a particular boon for the region.

Lettuce, especially Romaine, is still king, bringing local growers more than $600 million last year. But spinach has become increasingly important. In 2000, it was the 10th-most valuable crop in Monterey County. By last year, it had risen to No. 7, with a gross value of $188 million.

The current E. coli outbreak is at least the eighth food-poisoning episode traced to the Salinas Valley since 1995. Local growers were already working with the FDA to improve produce-handling procedures before the multistate outbreak occurred, Bogart said.

Each day the FDA keeps in place its nationwide consumer warning on fresh spinach costs the valley an estimated $1 million in lost sales.

The FDA’s Brackett said California growers need to do more to eliminate contamination.

“What we would like them to do is take ownership of the problem,” Brackett said. “The fact that this keeps coming up suggests that whatever has been done is not good enough.”