Spur of the moment camping, please help!!!!?

A group of girls, myself included would like to take a spur of the moment camping trip for a single night. It's too late to make reservations, all we need is a place to put up a tent and a place to make a fire (having firewood would be helpful). we are no frills. However being new to Colorado we don't know where we can go? can anyone help? Also, we don't like the idea of camping on top of other people, so crowded, "pack em in" campsites are not appealing. AND we don't want to drive more than 2 hours out of Denver