Well, 2nd Creek is right by Denver International Airport, just NE of the city. Coors Field is right in Denver. There is another track, Pueblo Motorsports Park, that is south of Colorado Springs, but I don't really have any info on that track. I'm kinda leaning twords the 2nd Creek idea for the group, but I will be going to the autocross as well.
AZ-SVT: you guys are MORE than welcome to come out! We had Jose from the Utah forums drive out for our last track day at 2nd Creek with his wife and it sounds like they had a blast. There are several hotels within 2 miles of the track, due to it's proximity to the airport if you need a place to stay. I'm sure that if you guys road triped up here, we would find something fun to do.
Alex in Boulder