BMRA details...
Here's a couple of posts for info I got on Barnwell Mountain before our August run.
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Having read those, I have some stuff to add now that we've been there.
The showers suck, to be precise. The water pressure goes from just enough down to a trickle and then back up again. If you time it right, you can get most of the shampoo out of your hair.

This may not be a problem if it's not too hot and you (like me) think camping means taking a shower when you get home.
The food vendor is pretty good. Better than balogna and easier than driving all the way into town.
The "clearly marked trail system" is a joke. There are good signs, but unless you've run the trail before, you will get lost. Plan on it. Scout ahead before making a turn so you don't get in over your head.
If you stay Friday and Saturday nights, buying a membership is only $5 more than paying the non-member fees. Then, it will be cheaper when you come back.
Bone-stocker first-timers can do several of the trails out there. Even some of the harder trails have good by-passes. Swak's one-wheel drive could do most of the easy (two diamond) trails with minimal strapping.