With the half dozen rides I've done in St. George, I think Sojodave is on the money with the Veyo area.
I like Hwy 91 from Ivins to Gunlock to nearly Veyo and back.
I also like Hwy 18 from town to Veyo and back. I've heard Snow Canyon is a tight descent for what it's worth.
Looking at a map now, you can easily make it a loop.