I appreciate all of the replies and I am going to look into the Sandhills, I had not even thought of Neb.
Does anybody know much about the Wasatch Mountains in NE Utah? That area looks like it has potential. My Benchmark shows a decent amount of 4x4 roads up in those mountains, and I found some hotsprings.
The Neb. option is nice because there is no snow concern lower.
Thanks everyone, keep 'em coming.
Glad to contribute, brp.
I've spent considerable time in the Wasatch Range in the immediate vicinity of Salt Lake City and Park City. There, the range is VERY rugged and excepting what are established roads up Big Cottonwood Canyon and Little Cottonwood, and the Alpine Loop which goes from Robert Redford's Sundance up and over to the Provo area, I don't think there are any through routes between Provo Canyon and Parley's Canyon (I-80), nor between Parley's and the I-84 canyon (Weber Canyon?). Oh, and the road up Little Cottonwood does NOT go through, period. The road up Big Cottonwood traverses Guardsman's Pass and it's of course seasonal. Shouldn't be too difficult to determine status from Utah local sources.
North of I-84 I've never spent any time poking around, but the Snowbasin Ski resort lies between I-84 and Ogden Canyon, so I suspect there's zero "through trail" potential there. There's a popular hot spring directly on the road which goes up Ogden Canyon towards Eden Reservoir. Several more in the Wasatch, but I think they're mostly heavily-used given the high population density of the Logan-Ogden-SLC-Provo corridor.
For the Sandhills, I heartily recommend two navigating resources: A copy of the DeLorme Atlas and Gazetteer for Nebraska and the series of 4 Cherry County Road Maps, available from the Nebraska Department of Roads. According to a phone conversation I had with the Roads Commissioner for Cherry County back in 2010, the various GPS/mapping software vendors routinely send folks on a wild goose chase down sand roads, where they get stuck and only then discover there "ain't no cellphone coverage". He assured me his road maps show only drivable roads, and when you put the road map up against the DeLorme, you get the picture that many of the roads shown on the DeLorme are not readily drivable. Another local also encouraged me to just head up any ranch road which may appeal, stopping at the first or nearest ranch house to ask permission, which she assured me would be uniformly granted.
There are big canoe/kayak/shuttle outfits in Valentine, NE, and one down in Mullen, NE, for the Niobrara and Loup/Dismal Rivers, respectively. The outfit in Mullen includes "tanking" trips on the Loup, where you and a gang of others float the Loup in large galvanized stock watering tanks. Looks like a hoot, and they pick you up and take you back to Mullen, where your rig or a motel awaits, enabling a few cold beers along the way.
In case it's not obvious, I was blown away by the one day I spent traversing the Sandhills, on pavement, at that. Can't wait to go back and spend a week or so.
Foy