For those of you in Colorado (or western Kansas or northern New Mexico or western Oklahoma or even northern Texas ), I've written an article for Crazy Guy On a Bike about the Purgatory River dinosaur tracks in southeastern Colorado. This is a mountain bike trip that can be done in a day but is better with an overnight camping stay on the edge of the canyon. The trackway is one of the largest in the world and demonstrates herd behavior of apatosaurii as well as hunting behavior by an allosaurus. There are also prehistoric and historic sites with in the canyon that are worth the trip.
September to late October are perfect times to visit. The days are cooler. Bring your favorite goat head protections, however. The goat heads are as epic as the ride!