Chuck might have a much more detailed answered than what I can give since he's actually in the area. Thanks to the logs he's been providing from the area I can at least give an overview of the area.
I would say the primary two sites you might want to take a look at are 211 - Sunlight Peak (Glenwood Springs in the DB) and 226 - Glenwood Springs (Glenwood Springs 2 in the DB). 226 is right above Glenwood Springs, so you're more likely find City specific traffic on that site. 211 will give you better coverage for Carbondale from what I've seen. As for CSP, it looks like 4C generally affiliates with 211 and 226, however it looks like there are periods of time throughout the day and late at night where units roam and end up not using one (or both) of the sites, especially very early in the morning. You might want to note that Garfield County law uses mixed encryption, so you'll find units using encryption while dispatch is in the clear.
As for traveling on the interstate, you might find
Colorado DTRS Interstate Travel Reference to be helpful in programming for the drive.