Yeah, the link to Goose Gossage's speech above is pretty accurate. The accent is a mix of Southern/Western and a bit of California Valley, similar to the younger skater/boarder types.
In Denver and along the Front Range there's also a mix of Mexican-American accent and Southern/Western drawl. It's a slurred speech with shortening of the words. Not everyone speaks that way. It might be an adaptation to the huge number of outsiders with their proper American English. Most linguists probably don't get it because they're in their sophisticated nest far from the local folks. But when two locals get talking, look out! The "a" has a bit of a twang and some consonants aren't pronounced.
For instance, mountains is /mow-ens/ with the /mow/ part rhyming with cow. The a in Colorado, when pronounced by a real local, sounds like the first a in radical and the r is heavy, round, and a little drawn out.
Mostly the middle consonants are skipped (except for the r) and the vowels are drawn out, but not in the "singing" way of a southern accent. They're drawn out in a twangy cowboy or western way. At least that's the way it is among the locals, who aren't really found in much in Denver anymore. They're in the suburbs and outer cities of the Front Range. Longmont and Loveland have a lot of locals, as does Colorado Springs, Pueblo, and the north Denver suburbs like Westminster and Arvada.