Knolls Recreation Area
Located just off of I-80 in Utah's west desert is the Knolls Recreation Area. With nearly 36,000 acres of sand dunes, hills, and mud flats, this place is the perfect OHV play area. The dunes are not as large as Jericho but just as fun. If your looking for speed the mud flats are the place, you can drive long distances on these flats and rarely feel a bump.
For a casual ride you can explore the many Knolls which the area is named after. There are trails going in every direction, pick one and explore the desert at your own pace, however while exploring this area be sure to stay in the boundaries. If you travel south you will come to a fence, if you cross this you will be entering the Dugway bombing range, not a good place to be. So stay in bounds and watch for the fences, which are clearly marked, and you'll be ok.
When planning your trip to this area there are a few things you need to keep in mind. This place is very desolate so bring plenty of water, food, etc. This is also a very bad area to have an accident so be careful because accidents can and do happen when you least expect it. On our trip my wife rolled her four wheeler and broke her collar bone. You feel pretty helpless out in the middle of the desert, and it can make for a very long drive to the hospital. Luckily it wasn't a life threatening injury, but it is going to hurt for a while.
Directions: To get to the Knolls Recreation Area travel west on I-80 towards Wendover for approx 1 hr 45 minutes, until you see the Knolls exit signs