In modern political terms, the hundreds of thousands of people left homeless by Hurricane Katrina are considered "environmental refugees" -- people forced out of their communities not because of a tyrannical government or violent civil war but because of a natural disaster.

The last time Americans saw so many environmental refugees in their own country was 70 years ago, when drought cast several hundred thousand people -- known colloquially as "Okies" and "Arkies" -- out of their Great Plains homes. Most were poor even before they lost their livelihoods; insurance was a luxury for the rich. They couldn't stay on their foreclosed farms, but most had no skills besides farming. Many, like the Joad family of John Steinbeck's novel, "The Grapes of Wrath," packed up their few worldly belongings in their jalopies and headed west.

No one expected the federal government to alleviate these people's suffering. The country was in the grip of the Great Depression, and food stamps, Medicaid and most other large-scale relief programs hadn't been invented.

These unlucky citizens had been dealt a fistful of bad cards. Some would survive the blow, some wouldn't. A few drifted toward cities, hoping to find factory jobs. Thousands of others fled to California, to seek work as "fruit tramps," or crop pickers, in the state's burgeoning agricultural industry.

Without money to pay rent (and no chance of getting credit without a job), the migrants set up squatter camps, often called "Little Oklahomas" or "Hoovervilles," rough-hewn shacks alongside roads or close to towns where they could get supplies. "They lived in conditions of almost unimaginable filth," wrote a journalist in 1937. "They were festering sores of miserable humanity."

Whole families worked in the fields, earning barely enough to feed themselves. When one crop was harvested, the workers moved on to the next. Most Dust Bowl refugees were of Anglo-American descent, and they tended to be conservative in both politics and religion, even though they often were labeled communists.

David and Sophie Krause and their 10 children moved from Idaho to California's San Joaquin Valley in 1934 and began working as seasonal laborers. Although they lived in abject poverty, they weren't eligible for public assistance because the state required families to live in one place for at least six months before applying for aid. The Krauses, wrote a social worker, were "honest, industrious, fundamentally healthy ... potentially useful citizens who are facing starvation, and there is no machinery to deal with their problems."

The Dust Bowl refugees also faced the anger and contempt of many Californians, who watched as their state filled up with poor, often uneducated, unskilled and unhealthy refugees. "It is as if the entire population of Cincinnati were to visit Cleveland, and, once there, decide to remain indefinitely," complained one journalist. By 1936, some California police had begun turning migrants away at the state's borders. James Davis, head of the Los Angeles Police Department, ordered his officers to arrest "all persons who have no definite purpose for entering the state, and are without visible means of support."

To many Californians, wrote Frederick Lewis Allen in "Since Yesterday," "these ragged families were not fellow citizens who had suffered in a great American disaster but dirty, ignorant, superstitious outlanders, failures at life. This engulfing tide of discontent must be kept moving."

Eventually, President Franklin D. Roosevelt set up the Resettlement Administration, over the objections of some in Congress and some political groups, and began building camps for the refugees. These Migratory Labor Camps, like the one nicknamed "Weedpatch Camp" in Arvin, Calif., were a cluster of one-room tents and tin shacks with shared bathrooms and laundry facilities and sometimes a nursery or medical office. "Boy, I thought we had a mansion," remembered a woman who lived in a tin cabin at the Arvin camp in 1945. "We got orange crates and put them up for cabinets. And the House Inspector would come by at least once a month."

Although many children worked in the fields, some attended local schools, where they were called "hobo brats." "These camps," proclaimed the school superintendent of Brawley, Calif., "are another example of the evils of a paternalistic government. The students who come in here from the camp are getting accustomed to clinging to the government's skirts. What will become of their initiative?"

The Resettlement Administration, under the leadership of Rexford Tugwell, did something else for the Dust Bowl refugees. It hired photographers such as Dorothea Lange, Ben Shahn and Walker Evans to produce a pictorial record of the Depression's effect on the rural poor. In a 1965 interview, Mr. Tugwell explained why: "Because this was so dramatic, and because it meant misery and tragedy for so many families, and because we hoped it would never happen again, at least not in the same way, we thought we ought to have a record of it for future generations ... and also to show people who weren't involved in it how extremely serious it was."