I can't help you on where to go but just remember that the prairie rattlesnake is considered a small game animal and you need a license to hunt them and there is only a 2 month season to hunt along with a bag and possession limit.
Critter is right, there is a season and bag limit. I don't know the details, but you can find out easily enough on the Colorado Parks and Wildlife website. There are tons of rattlesnakes in the northwest corner of the state. Find a little water with rocks nearby and you'll be lucky not to step on one. Don't look at the highest elevations.
There can be too much of a good thing with antler rattling.
I like to hit the horns together for a good 30- to 40-second rattling sequence and then hang them up and resist the urge to hit them again.
This works to the hunter's advantage, because if a buck has heard it, he may have been 300 or 400 yards away and he comes in and he's not exactly sure where it came from.
When finally is time to rattle again throw a slight change-up into the routine.
The second time, don't rattle as loud...