[recycled sixtie]

I agree with drcoastline it is not worth the risk unless there is a remote and you can operate it and not be in the line of fire if it lets go.

Can you not cut the wood in the ravine into small manageable pieces with a chain saw and bring up the small pieces with an off road machine that can climb the slope? Perhaps the slope is too great for that?

Safety first though. The other suggestion of renting a heavy duty skidder sounds good.
A hired hand or friend could help out for a couple of days to ease the workload and provide an additional level of safety.