Flight
SLC is closer to Boulder Mountain Guest Ranch 4.5 hour drive from the airport to Boulder.
Flight
Las Vegas is farther from Boulder Mountain Guest Ranch, however, driving from the southern part of Utah allows you to pass through some iconic state parks (Zion, and Bryce Canyon). Also keep in mind that Las Vegas is slightly more cumbersome and hectic to arrange- with rental cars, hotels, etc. 7 hour drive from Las Vegas, through Zion and up to Boulder