Roy, this is May 1955.

This photo was taken by Loomis Dean while on assignment for Life Magazine in Spring '55. Moulin Rouge, Dunes, Riviera, Royal Nevada and New Frontier were all opening around the same time. Just a few years back Time/Life published a bunch of these photos online for the first time. Here's a few others
http://time.com/3879776/las-vegas-photos-from-the-gambling-capital-of-the-world-in-1955/

And a couple others of Moulin Rouge
http://vintagelasvegas.com/search/loomis+dean+moulin+rouge