Of course you can make arbitrary divisions but that doesn't mean they are relevant. Not that the US can't be divided, but these lines aren't it.
The central-southern part of Florida has little in common with Kentucky nowadays. Phoenix, Las Vegas, Denver and Salt Lake are large metropolitan areas with cultures very different from rural Alaska.
Denver has an impressive light rail system, and Denver / Boulder are responsible for Colorado being one of two states first in legalizing Marijuana and the first in allowing public sales (though Washington state shouldn't be far behind once regulations are finalized). Polyamory doesn't have much public acceptance but is fairly common in the area. Programs and policies concerning homelessness are very progressive compared to most anywhere else in the US.
Denver/Boulder metro area, and to a lesser extent other communities along the Colorado Front Range, have much more in common culturally with SLC than Grand Junction, CO (the state's western capital) or any of the rest of the supposed "Empty Quarter". Peter Warden's Mormonia (if including Denver), being completely surrounded by the Nomadic West, is a more accurate division, though the name is a little inaccurate and not especially representative (at least half of SLC isn't mormon, and neither is most of the Colorado Front Range, though Colorado Springs is very evangelical).
If Joel Garreau still thinks Denver/Boulder and SLC are "Empty Quarter", and at least not aberrations, he doesn't understand the culture very well. It's almost as bad as placing most of NYC within "The Foundry".