Regarding the question of "Rhino Friendly" trails, in the southern part of the state (not national park land) the majority of trails are ok. The Casto canyon trail I mentioned is 50 inches or less, and some of the nicer trails on the Paiute are gated for ATV only which is 50 inch or less in Utah. They're mostly mountain trails though. Most of the stuff on the High plains or desert areas is open to larger rigs to include jeeps.
One thing to watch for is national park boundaries. Even if your ATV is licensed for streets, it's illegal to ride them in the national parks. In places like canyonlands, or capitol reef, you can easily ride a dirt road that will cross national park boundaries if you're not careful. Sometimes there are signs, sometimes they're missing. Either way it's a ticket if there is a ranger around.