An American Exodus is a documentation, in photographs and text, of the mass migrations of the 1930's caused by changes within the regionally varied agricultural traditions throughout the country. Photographer, Dorothea Lange, and writer, Paul Schuster Taylor, subtitle their work A Record of Human Erosion. Yet, the presence of land predominates over people in both image and text. Human erosion is recorded in the images and terms of erosion of the land and erosion of agricultural traditions. The human condition becomes the condition of the land in this sleight of hand which ultimately portrays the symbiotic relationship between humans and the land in America.

Lange and Taylor document two types of migrations. One is the migration of agricultural workers to urban centers and often back again to rural areas. The other is the migration of agricultural workers Westward. Both types are caused by changes in agricultural practices. In the South, plantation systems were replaced by sharecropping while in the great plains and the midcontinent individual ownership was replaced by tenant farming which was itself made next to impossible for most by agricultural depression, drought, and the effects of long term abuse of the land. While the text explains the failures of land and agriculture, the photographs can't help but express the largess of the land, even as they too document its failure. This results in a tragic sense of wasted potential and broken promise in this record of a people with no place to go in a land so large.

Both sharecropping and tenant farming put the land and decisions pertaining to it in the hands of a small class of owners. Generally, these owners had little sense of responsibility to their workers and cash incentives from the government to make use of day and seasonal labor. Farm and plantation owners could avoid sharing profits with their workers by paying them by the day. Thus, workers were denied the security of a job not dependent upon season and limited by competition. In the South, workers commuted from towns to farms and plantations for a day's wages. In the West, families followed the work nomadically as the end of seasons meant the end of temporary employment on large-scale farms.

In addition to the change in ownership and labor structures, mechanization was also responsible for migrations. Improved technology, particularly the tractor, meant that more could be done with fewer people. This limited the amount of work to be done by humans on farms and plantations. Many workers moved either to the city or Westward. Arriving in the city, workers found all too often that technology made human labor less relevant in industry as well as agriculture. Instead of finding jobs, they found themselves sitting and waiting for work.

From Arkansas to Texas and Oklahoma, many workers chose to trek Westward in search of work in California and other Western states, promised in ads declaring that thousands of workers were needed. This story, made familiar by Steinbeck's portrayal of the Joads in The Grapes of Wrath, is known too well to repeat it here. Lange's photographs of families on the road, packed into cars and wagons loaded down with home's belongings, however, tell the story in a visual and powerful way.

Finding no more work in the cities than in the country, many workers returned to the farms and plantations. Likewise, finding less work and a harder lifestyle than anticipated out West, many returned East again, some only to trek back West once more. In a way, it seems only fitting that all this strained movement should result in the lines of make-shift dwellings that wended the roads like so many scars of human erosion. It was, after all, the land itself which in so many ways forced the migrations in the first place.

Such temporary towns were the signs of what Taylor calls a "large, landless, mobile proletariat" developing in the West out of the mass of large-scale farm laborers. The documentary ends with a brief look at the organization of such workers into striking unions and ultimately poses some suggestions toward reform. They point to the inadequacies of the relief projects in operation at the time, call for "comprehensive congressional action", and place their hope in industrial expansion.

Ultimately, this documentary offers two views to its 1939 audience not yet quite removed from, but becoming ready to take stock of, an era of depression. First, it locates these migrations within a larger history and tradition of American migration. These migrations are made the latest versions of challenges of the wilderness to a pioneering people. This renders the challenges of the thirties surmountable by placing them in a tradition of similar challenges that had been surmounted, by putting the end in sight, and by offering some historical distance. This also lends the migrations an aura of respectability and even reverence by identifying them with a patently American desire to, like Huck Finn, light out West. Secondly, though Lange and Taylor speak to the responsibility of humans in shaping the ways land is used and labor is structured, the project depicts human erosion as a consequence of powers of land and agriculture beyond human control; it is, after all, an erosion and not a failure:
These people are not hand-picked failures. They are the human materials cruelly dislocated by the processes of human erosion. They have been scattered like the shavings from a clean-cutting plane, or like the dust of their farms, literally blown out.
In a materialistic gesture, oddly foreboding of that view of humanity which would literally scatter people like so much material or mortal dust in the ensuing war, Lange and Taylor seek to come to terms with the changes and conditions of the 1930's which displaced people in thought as well as in body.