The Great Depression is, for many Americans, a memory that has become a photograph. Out of the chrysalis from which history emerges have come Walker Evans's photograph of a sharecropper, Dorothea Lange's ''Migrant Mother,'' and Arthur Rothstein's ''Fleeing a Dust Storm'' - examplesof history-turned-photograph.
For those who lived through the depression, the picture is larger, the context fuller.
These people have stories to tell, the sort of stories that our standard history textbooks - the books illustrated with photographs by Evans and Lange and Rothstein - don't quite do justice to.
Not that they're wrong, these textbook tales, but they're just not as real as a book like Bill Ganzel's ''Dust Bowl Descent.'' His exceptional work puts back a lot of the heart that was missing, enlarges the context through which we can more fully experience the depression.
''My father had told me about growing up in the Depression,'' writes Ganzel in his introduction. ''Sitting in living rooms in Felt, Oklahoma, or Williston, North Dakota, people told me hundreds of stories about the hard times they had been through, and I began to realize that I was not hearing merely the stories a parent tells to unimpressed children - that, for thousands of people, my father's stories were typical and true.
''Through these people who had survived a terrible social upheaval,'' he continues, ''I began to understand the depth of the human costs of the Depression.''
Ganzel's book was a long time in the making, for he traveled all 10 Great Plains states interviewing people and making the photographs which ignite ''Dust Bowl Descent.''
Ganzel searched out the same, or sometimes similar, places where Farm Security Administration (FSA) photographers like Russell Lee, Dorothea Lange, and John Vachon had planted their cameras decades earlier.
He was ''groping,'' he writes, ''toward a broader definition'' of his subject than ''that is how we were then, and this is how we are now.''
Ganzel was wise not to attempt merely to replicate the vantage point, lens angle, and other technical considerations of the classic depression-era photos. Consider, for example, his photograph of Florence Thompson, the woman most of us know only through Dorothea Lange's classic image as the ''Migrant Mother.''
Ganzel found Mrs. Thompson still in California, and he photographed her and three of her daughters in 1979 in Modesto, some 43 years after Lange made her image of Thompson.
Here is what Florence Thompson told Ganzel: ''When Steinbeck wrote 'The Grapes of Wrath' about those people living under the bridge at Bakersfield - at one time we lived under that bridge. It was the same story. Didn't even have a tent then, just a ratty old quilt.
''I walked from what they'd call the Hoover camp at the bridge to way down on First Street to work in a restaurant for 50 cents a day and leftovers.
''They'd give me what was left over to take home, sometimes two water buckets full. I had six children to feed at the time.''
Florence Thompson's daughter, Katherine McIntosh, told Ganzel: ''She worked hard, brought us up and kept us together. We all have good jobs and we all own our own homes. And none of us has ever been in trouble.''
''Dust Bowl Descent'' is full of such simple eloquence, along with page after page of photographs juxtaposing the FSA images of the late 1930s and early '40s with photographs Ganzel took between 1975 and 1980, as he crisscrossed the Great Plains.
Ganzel puts all his findings in context, offering comments by those photographed, and including historical information as necessary.
But this is not a text-heavy book.
It doesn't need to be, because the photographs carry the weight of Ganzel's compassionate vision.
''Dust Bowl Descent'' is an extraordinary book - an obviously personal work that has found the soul of its subject - an evocative history that brings its subject back to life. I'd call it a work of love.