Refer to the passage. "Contrary to many published reports, a good many people had left this country either temporarily or permanently before any rains came. And they were not merely ‘drifters,’ as is frequently alleged. In May a friend in the southwestern county of Kansas voluntarily sent me a list of the people who had already left their immediate neighborhood or were packed up and ready to go. The list included 109 persons in 26 families, substantial people, most of whom had been in that locality over ten years, and some as long as forty years. In these families there had been two deaths from dust pneumonia. Others in the neighborhood were ill at that time. Fewer actual residents have left our neighborhood, but on a sixty mile trip yesterday to procure tract repairs we saw many pitiful reminder of broken hopes and apparently wasted effort. Little abandoned homes where people had drilled deep wells for the precious water, had set trees and vines built reservoirs, and fenced in gardens—with everything now walled in half buried by banks of drifted soil, told a painful story of loss and disappointment.”

Excerpt from a June 30, 1935, letter from Caroline Henderson of Eva, Oklahoma, published in the Atlantic, May 1936

Which of the following US regions was most affected by the migration spawned by the environmental disaster highlighted in the passage?

Virginia’s Shenandoah Valley
Louisiana’s Mississippi Delta
California’s Central Valley
Oregon’s Columbia River Gorge