Los Angeles - Kerne Erickson?
If this is a Pan Am poster, it clearly falls into the "By Clipper" category. That said, San Francisco was the major California hub for Pan Am in the 1940s, the Pan American logo doesn't look right and this poster art can be found with TWA branding, all suggesting that this is likely an imitation Pan Am poster. In fact, a close inspection of the original TWA poster and the Pan Am version reveals that the art is slightly different, so this is not a case where two airlines used the same art. Perhaps a Kerne Erickson poster.
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