Although it wouldn't be the most appealling place for a hike, you might enjoy shooting on the Pawnee National Grasslands. This area is located in NE Colorado, approximately 30 min to 1 hour from Ft Collins (near Ault), with the drive time depending on where you want to shoot.
I haven't been there in a couple of years, but used to shoot out that way a lot when I was living in Ft. Collins. It is definitely one of your best bets for shooting long distance, and you can certainly find places out there where 1,000 yard shots are possible.