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.
Want a quick and inexpensive call for Moose? Take an empty 32 ounce coffee can, and make a small slit in the bottom, only about a quarter inch. Then, take one of those really big red rubber bands, the ones that go around big folders. Cut the rubber band to make one long piece.
Now, thread one end of the band and tie a knot on the outside of the can so it won't pull through. Cut the band off on the other side so it is even with the top of the can.
Now, wet your finger,...