Looks like the Lumbar Yard in Des Moines, IA. You can see part of the word Lumbar Yard in the background in one pic. Link:
http://www.iwantwood.com/schedule.htm
Calendar says they do it on Sunday nights. What I have been told it's just the girls from the club in the contests. If you look at a lot of the NAP pictures the Lumber Yard has most of the girls there. So you will probably see some of the same girls in these pics as at the Lumbar Yard.
Enjoy
Billy