As the Great Depression worsened, she began photographing people she saw on the streets: men curled up sleeping or in line for food. In 1935, she married the economist Paul Taylor; they left San Francisco together to photograph the living conditions of agricultural laborers up and down the state, from Davis and Marysville all the way to Imperial County. The Farm Security Administration supported their work.

“Mam, I’ve picked peas from Calipatria to Ukiah. This life is simplicity boiled down.” — From Dorthea Lange’s notebook

In 2017, I started reading Ms. Lange’s notebooks, now held at the Oakland Museum of California. On lined 3 by 5 inch pages, in penciled-in cursive, she captures American history in staccato fragments, jotting down what laborers paid for gas, rent and food; how much they could make picking a day’s worth of potatoes. On one June trip following the melon harvest in El Centro, under a heading “The camp,” she notes someone saying: “This is a hard life to swallow, but I can’t just rest here.”

“We come from all states and we can’t make a dollar in this field noways. Working from seven in the morning until 12 noon, we earn an average of 35 cents,” a worker told her in 1937.

“Not enough money for cotton sacks” reads another note; “All I’ve got is right here.”

“2 children 4-6.”

“Sold everything little by little.”

“We said we came from,” she writes in a note that ends in an eerie, indecipherable smudge: “They said, “Why don’t you go back there then?”

“This country’s a hard country” one woman told Ms. Lange. “If you die, you’re dead — that’s all.”

As a poet, I was drawn to the chorus of voices Ms. Lange recorded, which call across time. Her notebooks catalog concerns that feel sharply relevant eight decades later: the search for shelter, a fair wage and stable work.

Last year, from January to October, I drove across California, following routes Ms. Lange noted in her travels from 1935 to 1942, by which time she had been hired by the Office of War Information to document the process of Japanese internment.

As I visited encampments, internment centers and small agricultural towns, I used Ms. Lange’s images and words as a lens to help refract the messy complexity of California’s present. I grew up a mile from where Ms. Lange lived in Berkeley. My town, El Cerrito, populated quickly in the early 1940s by an influx of shipyard workers, has neat cottage bungalows with lemon trees on tight plots. Ms. Lange photographed these in 1942 as a hopeful emblem of the New California: an emergent middle class.

But the Bay Area today is no picture of middle class stability. My once modest neighborhood has skyrocketing home prices — a small three-bedroom that eight years ago cost $500,000 now lists for $1.3 million, while roughly 28,000 homeless people sleep on the streets in the Bay Area each night. Vacant lots, industrial blocks and underpasses nearby fill with semipermanent encampments. I bike my children to school each day through a maze of tents and trailers.

Following Ms. Lange’s images and notes has become a study in uneasy juxtapositions: rifts between enormous wealth and unsettled poverty, some of which feel new, some like a continuation of the past.

In Imperial County, which now has the highest unemployment rate in California, Eddie Preciado of Catholic Charities holds beds at the county’s one homeless shelter for men, offering shelter to migrant laborers who cross the border to pick corn.

“There’s still no dedicated housing for agricultural workers,” he told me. Down the road, a detention center run by Management Training Corporation for ICE holds 782 beds.

“Most middle-class jobs are in border security,” Mr. Preciado said.

In Nipomo, where Ms. Lange pulled over near a frozen pea field to make her famous photograph “Migrant Mother” in 1936, a new community of $1.2 million tract homes overlooks rows of factory-farmed strawberry fields edged with workers’ trailers.