To answer your question Scott
Here are a couple ideas/thoughts...
Why does the BLM require that someone else take the liability of the land they are all ready liable for? I have heard this in the past from the BLM/USFS (nothing official, just in passing). I guess I fail to see where they would be MORE liable because they actually promote recreation on the same property (seems counterproductive??)
Is Carbon County against taking liability for these trails? I can admit it doesn't sound too feasable from a couple standpoints for a County to take it over, especially your County which has done an AMAZING job for the 4x4 crowd (thanks to you!) already.
I would make contact with a couple different groups to see what their thoughts are:
1. Usa-All - they can tell you the legal standpoint of the liability,
2. PLEAA, I know they were instrumental in the new Shoshone trail system up North, not sure how they handled the liability end of things.
3. Marsha Terry (U4WDA Board Member), Marsha is on the Motorized Rec. board, and could probably help you guys get some Federal Grant money to make these trail builds happen, they have funded tons of other projects that quailify. Let me know if you need Marsha's email info...
Hope that helps