I believe that 1140 has gone through more format changes than any other signal in Las Vegas radio history. Here are my memories, feel free to correct me on the dates. I might even be missing a format or two.
Pre 1978: Top 40 KLUC. A simulcast of 98.5 (or FM 98 in those pre-digital days). They called themselves K-Luck. I heard the AT40 from April 1977 on KKLZ this weekend and it brought back fond memories of songs KLUC played back then (and played often) such as Climax Blues Band-Couldn't Get It Right, Kenny Nolan-I Like Dreaming, Jennifer Warrens-Right Time of The Night, and David Soul-Don't Give Up On Us. Dave Anthony did mornings, Dave Van Stone middays, and "Dr D" Rick Denton did afternoons. I believe Mike Bradley did evenings. In the early 80s he co-hosted a nightly TV show called PM Magazine. The contest KLUC ran for the Spring 1977 book (back when there were only two books a year) was the "KLUC Call Girl"..which was a cash contest.
1978-1986 Magic 11 KMJJ. This AC station was ahead of it's time because it was voicetracked, although it was live assisted. It wasn't boring tracks,,they had high profile personalities, such as Charlie & Harrigan, Rick Shaw, and Steve Goddard. I remember how good their music was. Some of the songs I remember them playing a lot in the late 70s include England Dan and JFC "Love Is The Answer", LeBanc and Carr "Fallin", and Rex Smith "You Take My Breath Away"...they had a good selection of gold too such as "Kentucky Rain" by Elvis.
1986-1988 I believe they ran an oldies format from the Satellite Music Network. KENO was also running a satellite oldies format from the old Transtar network.
1988-1989 Heavy Metal KRSR "The Krusher". In 1989 at the peak of the metal craze Las Vegas actually had two hard rockers on AM...1340 was a Z Rock affiliate.
1990-1993 They went back to simulcasting 98.5
1993-1997 "Casino Radio". A station aimed at tourists. 24 hours of hotel and show information. They worked out a deal with some of the rental car companies to set 1140 on the car radios.
1997-1999 Sports, as someone mentioned they ran the old Sports Fan Radio Network..which explains the KSFN call letters.
1999-2001 Crusin Oldies. Over the past 15 years this was the format that pulled the highest ratings for 1140. I remember how most people thought it was a mistake, that there was no way anyone was listening to music on AM..yet they had a few surprisngly good books, so it could have been for real.
2001-2005 Hot Talk. They took off where the old 105.1 left off.
2005-2008 Spike "Radio For Men" but not too many men (or women) listened to it.
2008: Back to Sports. Some would say the market is oversaturated with sports radio. We may not have a pro team but we sure have plenty of sports gambling. Besides sports has one of the highest power ratios of any format.