Much of the main trail can be done with anything you want. It's a bit harsh on narrow road tires and wheels, but any old hybrid or MTB will do. There are times that I take the suspension fork off for just riding on the trail. There are however some offshoots where a hardtail with suspension fork is a bit more fun. You really only have to keep your eyes open for water cuts and runoff trenches that haven't been filled. For trail riding I use a hardtail with or without suspension fork and Kenda Kosmic Light II tires in a 2.0 size to ride on top of the gravel, limestone or dirt. That tire will allow you to get off the trail and do a bit of asphault riding if you wish. It's not enough for loose sand or deep dirt however as it starts to spin without traction if your going uphill.

My "access roads" are not however safe for a road bike or comfortable with a rigid fork. If I wasn't so cheap, I'd love to build a dual suspension setup just for fun. I had an old school one years ago with a coil/shock rear but I gave up on it quickly because it was a tank.