Streams will be difficult to find. There is a wonderful resevoir called Colob outside of Virgin (take a left and go 22 miles) that I'm very fond of. I caught m 23" cut from that a few years ago.
Also, the Quail Creek Resevoir between Hurricane and St. George is stocked with rainbows and largemouth. You can catch both on the same flies. The water is very rich, allowing for some huge rainbows and the rainbows allow for some huge bass. Again, a boat or floattube is optimal.
Frank Reid