We’ve previously seen a 1928 booklet with this same title. Though the booklets are just four years apart, they are completely different. The 36-page 1928 booklet has just one page of text, whereas half of the 52 pages of the 1924 booklet are text.
The front and back covers of this edition fold out to make a spread that is more than 20 inches wide, as shown below. Where the inside covers of the 1928 booklet are blank, the inside front cover of this one has a map of the Rock Island system while the inside back cover is a list of passenger agents.
There may be some overlap of photos, but if so I haven’t found them. The photo on page 2 of this booklet was probably taken the same day of approximately the same scene as the one on page 29 of the 1928 booklet, but they are different photos.
The 1928 booklet at least used turquoise to illustrate the sky on the cover graphic. This one appears to be a more realistic blue, though my copy is somewhat aged so it is hard to tell for sure. I suspect that phrases like “turquoise sky” and “sapphire sky” simply meant to suggest that these destinations had lots of sunny days.