If you are looking for a campground destination you can pre-book, only 2 hours outside of Denver I would suggest Green Mountain Reservoir. The only downside would be that most sites have little shade and the water levels at the lake were low at this time. There are other sites within the area, especially on the other side of the reservoir that provide more shade.
More Information:
http://www.greenmountainreservoir.com/
http://www.recreation.gov (search for Cow Creek North or South for reservations)