pri_dk, thanks for posting this map. I bookmarked it.
I discussed this “dust bowl” migration here before as it applies to San Diego.
These “American refugees” left their barren, windblown hometowns, stripped of all natural resources, in droves for CA, lured by wartime defense jobs advertised in their own local newspapers!
They packed up their families in station wagons and their trailers to the gills and headed west …. CA or BUST!
For instance, the Bay Park flats was an original settlement of defense workers …. almost ALL from Oklahoma! Now deceased, many of their small houses (with knotty-pine kitchen and built-ins, lol) have been passed down to their children and grandchildren.
Read stories of why these many thousands of Americans left the only home they ever knew to migrate west during that era:
They obviously felt they had nothing more to lose….