I was talking to a fellow trail builder this weekend (maintains and builds the mtu trails in Houghton) and he recommended using a soil mix called A23 which the DOT often uses. Its a great mix of clay, sand and aggregate. Boy only could it be healthy and stable for the beer run trail but in places of exposes roots and undesired objects in the trail. Just as effective as armoring and less work. We should see about getting a load of it. 
Keleney Top Soil will sell us the clay mix used for sports fields and moto events/facilities at same rate the city (Middleton) gets. Two professional trail firms and a bike park designer suggested we use this. Only exception was they said don't use aggregate because it's easier to shape and get blue groove.
Transportation is a big factor so the prices we have for small and large loads to Middleton would probably be more at Cam Rock. There may be a firm doing this that's closer.
I will be buying that mix at the bike park so you'll be able to check it out yet this season. The fill with clay at Blackhawk has aggregate and no more top soil borrow pits are allowed so you can check that out too.
