Not sure where the trails run through in relation to the tunnel, but it isn't too far off of the main road. It has been cleared out quite a bit so you can actually see it from the road now if you are looking for it. It's worth a look, pretty cool. I'm told there is another tunnel further down the line that can still be accessed, but i haven't had time to go look for it. Here is a link with GPS coord that might help.
http://www.moonvilletunnel.net/
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