This is the itinerary I would follow if I were on a road trip from Salt Lake City to St George:
- Salt Lake City to Bryce Canyon National Park (on I-15 and take Exit 95 for UT-20)
- Stay at one of the hotels in Tropic , UT (just outside Bryce Canyon National Park)
- Tropic to Zion National Park , overnight at Zion National Park Lodge or
- Proceed to Saint George and stay at Red Mountain Resort, St George: https://www.redmountainresort.com/
Hope this info helps.