In a June 1968 letter to Michael Barrier, Barks wrote about Al Koch: "He is the guy who led me to a bluff near Thousand Palms and showed me the ancient Indian trail that started the sequence of ideas that became the plot of the Seven Cities story. Al and I 'developed' the plot that evening over copious draughts of bourbon and ale."
In a February 25, 1976 letter to Marty and Elouise Martin, Barks wrote about the story: "You will notice some recognizable spots as Indio and the Colorado River in the story's locale. The tale grew out of a Sunday visit with friends, the Koches, who lived in Indio. Al and Evelyn took Garé and I to a place on the Thousand Palms road where an ancient Indian trail wended over a mesa. There we saw rings of stones, cremation sites, and most of all worn steps up the far side of the mesa that indicated the trail had been used for centuries by traders from the Arizona tribes and from the coastal Indians. Al said that in past years the area had been combed by artifact hunters who had cleaned out all the arrowheads, but we were able to do a lot of daydreaming about where the trail led, especially to the eastward. Al had heard of jeepers who had seen segments of the trail at spots all the way into Arizona. That night after several martinis Al and I began to put together the framework you will read in this comic.
The historical surmising about the lost ship of the desert, the final fate of Admiral de Ulloa, and the location of the Seven Cities came from some cursory reading of very old books in the Library at La Jolla a few years previously. Also I overheard a very long-winded liar in a restaurant one day telling of how he saw the lost ship one day in the desert south of Blythe just after the big wind storm.
Anyway, the tale results from more research that I usually devoted to my comic work. I included Al in the cast of characters. He is the wellfare official who is seen kicking the Beagle Boys out of the Indio office, which was his work in real life."
Geoffrey Blum notes that Barks did the research at the library in 1950, when he was researching the historical background of "In Old California" (OS 328-02). Al Koch is shown on panel 3 of page 12.