This quote from the Denver Biz Journal says it all:
"The chain's signature ButterBurger is made from ground chuck and sirloin that never are frozen. It gets its name from the fact that butter is lightly brushed on the top of the bun before it's toasted." http://denver.bizjournals.com/denver/stories/2006/07/03/daily26.html
When I get home to Minnesota, or drive through Wisconsin up to Lake Superior, Culver's is a must-stop. Not only are ButterBurgers to die for, but their frozen custard is the stuff of dreams.
There are Culver's in Colorado Springs -- if you drive I-25 south on your way to Santa Fe or Taos, there're a couple not too far off the highway. http://www.culvers.com
Looks like the Denver metro location will be opening up in Thornton. Well, now I have a reason to drive up to Thornton.