Nothing spoils the experience of being out in the back country than the noise of a motorbike which travels for many miles. We use our feet and on some trips our bicycles but I hope I am never so old and frail that I need a motorbike.
For desert roads/trails the Suzuki Brat and similar models from this company are amazingly good for serious offroading. I have seen them go places where Hummers (the GM non-military models) where having trouble though past of this was probably the ineptitude of the Hummer drivers who expected the car to make up for their own lack of experience and skill.