From the booklet “California,” of which more text is produced in a post below.

A dome coach ran on the City of Los Angeles and City of St. Louis, as well as on the Challenger when it and the City of LA ran as all-coach and all-sleeping car trains during summers and Christmas seasons.  Before the late fifties, when the COLA and Challenger were placed on the same schedule and ran as one train (COLA) most of the year, the Challenger carried the dome coach (once domes were added in 1955), and coach passengers on the COLA had to accept, as far as access to a dome was concerned, dining in the dome of the diner. My grandparents traveled from Chicago to LA in coach on the COLA, and my grandfather said breakfast in the dome on the morning the train arrived in LA was the nicest train experience he’d ever had.