Plumber32,
Well I guess we need a definition of what is "decent" riding. I like the Red Desert south of Lander, approx. 42 miles to our antelope camp. Look for Gold Creek (Simply a creek) to the west and Atlantic City (old gold mining town) to the west. It is mostly BLM with National Forest on the fringes. Riding is permitted on roads, there is a bar and grill in Atlantic city. Lots of rough camping opportunities, no facilties. Mostly two track, nothing hairy and not likely to break anything, if you stay sober but still possible. I wouldn't take my 35' Toy hauler very far in but a 4x4 pick-up could get to most places. Place is covered with wildlife especially antelope, and mule deer. Bear, including grizzlies and wolfs are on the periphery.
There are sand dunes not to far north of Rock Springs at I-80 and south of the Red Desert. I'vs been snowed on pretty hard on Memorial day and experienced the 500 year storm in Sept. It washed out the freeways.
Hope this helped.
s/f Steve