Fifteen of the California Zephyr ads I’ve found in National Geographic were cartoon ads. All were placed by Western Pacific, and in most cases the cartoons were drawn by Gerhardt Hurt, about whom little is known other than that he lived in San Francisco and illustrated at least one children’s book titled Scare Boy.

This 1950 cartoon ad from the New Yorker is signed (at the bottom of the top cartoon) “gh” for Gerhardt Hurt. This was also the only cartoon ad I’ve found that was signed by all three railroads and not just the Western Pacific. Click any image for a larger view.
The first cartoon ad I’ve found appeared not in Nat Geo but the New Yorker in 1950. It focused on the health of long-distance passenger rail travel in the face of airline competition. I’ve also found cartoon ads in the New Yorker and other publications that differed from any in the National Geographic series, and Hurt also did at least one cartoon ad promoting Western Pacific freight service.