He was accorded a great deal of latitude in illustrating articles for Popular Science Monthly on topics such as an automated freeway, a futuristic city, and "How The World Will End".

Seielstad married Nathalie Pomeroy around 1912 with whom he had a daughter, Lucile, born in Los Angeles in 1914.

[6] In the 1930s he illustrated numerous articles in Popular Science Monthly for which he produced drawings showing the technical aspects of products such as a cutaway of a pocket watch (1931),[1] as well as others showing forecast and speculative scientific developments such as a future city (1934) based on the ideas of British writer R. H. Wilenski which envisaged cities composed of buildings on slender trunks like trees.

The degree of license given to Seielstad in interpreting the article text was reflected in Popular Science's comment "our artist presents here his conception of this startling proposal".

[2][7] He also drew an automatic freeway (1938)[3] and produced four illustrations for an article titled "How The World Will End" (1939), one of which showed a "giant meteor"[a] about to hit New York City and the city's inhabitants fleeing for their lives:[9][10] By 1940, Seielstad was working for Life magazine and was pictured at work in their 1940 issue commenting that the events of the Second World War were like his first job covering the San Francisco Earthquake.