Okay... well... that is not Central Illinois, but rather North Central... a BIG difference in terrain between the two -- thus my confusion.
I do not live too far from that area, and frequently ride (and drive sometimes) the length of the Rock River from the Rockford area down to Dixon. It is one of my many stomping-grounds; so I am very familiar with the area.
Don't know if you are talking about the "Stronghold Mansion" near Oregon, IL or not. If so, that road is one I have always wanted to go up to see the old mansion there; however that road is nearly impassible on the Spyder... at least it looks like it at the bottom where it turns real-sharp on a steep incline (which sounds like what you are describing). (The mansion is owned by a church and they have summer camps and events there.)
There are a lot of areas all along the Rock River though that have similar gravel/dirt roads that are steep, and almost straight-up from the river to the bluffs. Some of them I would not attempt to go up on a Spyder. You would have to be the judge to the specifics of the exact road you are talking about.
However, if you would be a bit more specific with your information, I could give you a more definitive answer, since I know the area very well. I would be happy to do that for you. :thumbup: