LBL is approximately 2500 acres but there are around 100 miles of trails packed into that area. That is taken from the web site:
In my guesstimation I would say that about 40-50% of it is fairly rocky. There is some hard pack sandy, gravel type stuff (the main outer loop), some nice black dirt (mostly in the valleys and bottoms) and lots of hills. You can go up & down, up & down , up & down all day if you want. Lots of medium sized hills (no giant ones) but plenty tough enough with rocks, roots and/or loose soil.
I would drive 8 hours to ride there at least once just to check it out. Its only about 4 hours for me but I've been there 3 times (i think) in the last year.
One note about the quads, buggies etc. - you can (for the most part) get away from the areas that those folks spend most of their time and not have to worry too much about them.