After working in New York for several years post high school — and taking a class at Columbia University with the famed art photographer Clarence H. White — she decided to take off on a trip around the world with a friend; a pickpocket curtailed their ambitions and they never made it farther than California. Lange would live there for the next half century. Despite her brief experience with White, she was mostly self-taught, trained in the commercial demands of commissioned portrait photography, whose wealthy subjects sat for her in a rented San Francisco studio. She grew into her aesthetic style and moral motivations, which came to her, together, at once. She was still married to her first husband at the time, an esteemed landscape and mural painter, and her two sons were young. It was 1933, and the Great Depression had reached its lowest point. Lange looked out the window of her studio, where her wealthy and safely ensconced patrons sat, and saw the ravages of joblessness and hunger on the streets below. It was then that she took her first documentary photograph, “White Angel Breadline,” which today remains a kind of visual shorthand for food scarcity during the Depression.

This single image — of a group of downtrodden men, all with their backs to the camera except one, whose dirty face is looking hopelessly at the ground — would position Lange alongside Woody Guthrie as a primary witness to America’s decline in the 1930s. With her camera she would capture remarkably intimate images that were universal in their communication of shared suffering: an oddly thin baby nursing at his mother’s breast inside a homemade tent in Blythe, Calif. (“Drought Refugees From Oklahoma Camping by the Roadside,” 1936); a man sitting beside an upturned wheelbarrow, his head bowed low in desperation (“Man Beside Wheelbarrow,” 1934); two laborers walking down a long and empty dirt road with perhaps all they own in their hands, as they stride past a mocking billboard advertisement for the Southern Pacific railway that reads “Next Time Try the Train, Relax” (“Toward Los Angeles, California,” 1937).

Not long after abandoning society pictures, Lange was separated from her husband and working alongside Paul Taylor, a Berkeley agricultural economist whom she would soon marry. The California State Emergency Relief Administration hired Taylor in 1934 to study migrant workers, and he convinced them to hire Lange in 1935, sneaking her onto his research trips as a typist, knowing very well that she would, in fact, be photographing everything. They traversed the state and together devised a new kind of multimedia sociology, one that was part oral history and part visual documentation. Sometimes their tactics were wily. In Arizona, Taylor got a running count of migrants by hiring a gas-station attendant to clock them. His figures, alongside Lange’s photographs of extreme destitution and hopelessness, were the first records of what would become known as the Dust Bowl, the name given to the drought-choked Southern Plains. The physical image we retain of this era was almost single-handedly shaped by Lange. Her initial joint report with Taylor was spiral-bound and included over 50 of Lange’s photographs. These were bureaucratic reports conceived like novels, with Lange capturing the sort of detail no pie chart could render — the decaying roll of linoleum, for instance, that a homeless family had been carting around for three years in hopes of once again having a kitchen floor.