Chicago Great Western RR

There were no advertisements in the National Geographic for the first few years of publication (starting in 1888).  Then in 1896 they began a regular monthly issue that included advertising.  Many of the early ads were from railroads selling trips to California.
Ads used to be real talky: sometimes paragraphs of sales points and descriptions.  There weren't a lot of photographs in the early issues; neither articles nor ads.  The railroads might include a postcard view of a pretty mountain and river.  This is one from 1897 of the first ads with a prominent illustration of, wouldn't you know, a pretty girl.