I would guess early '50's but that just based on that the graphics on the menu seem to me at least to be more 1950's than '40's...El Rancho Vegas was the first hotel-casino on the Strip. It opened on April 3, 1941.....
A kangaroo fight is seen in this March 15, 1985 photo at Circus Circus in Las Vegas. Referee Betty Krause moves in to separate Boomer and Carol Pullman during a match. The kangaroo fought several times a day. (Wayne Kodey/Las Vegas ***************)