It's not Moab, but there are plenty of fun trails and free riding opportunities. This unimproved road starts off of Hwy 24, west of Hanksville. It is close to the Mars Desert Research Station, please stay clear of MDRS during simulations. Take this one north up to BLM Road 0110, which is considered a primary road, which can be ridden down to Hwy 24.
For more information on MDRS, see their site: marssociety.org