Here is everything you ever wanted to know about shooting rifle competition in AZ:
http://arizona.rifleshooting.com/
If you have an M1A, you are probably best off using that rifle in "service rifle" matches. Those allow only iron sights, but the rifle is well-suited for the job. Here is link for that:
http://arizona.rifleshooting.com/nmc.html
or this one:
http://members.cox.net/riohighpower/