Utah lies about 30 miles to the east of Mesquite, and St. George is the first city inside Utahs borders. I see a lot of Utah license plates in Mesquite, like I see a lot of California plates in Vegas. I think it is a convienient retreat for folks in prudish Utah.
I usually pass thru Mesquite on my way to Colorado, but it is about the same distance to Salt Lake City too. I used to make the drive in one quick swooping motion, but I've aged and it has become neccessary to make it in two days. I like to stop off in St. George and maybe take a side trip out to Zion Canyon National Park. The side trip is about 2 hours out of the way, but the scenic drive through Hurricane is pleasant.