rfisher99 asked:
I need to build a bridge over a small gully / brook to get a Honda FOreman ATV over. It needs to be 11 foot long and near 10 foot wide and support the ATV, me 200lbs, and a trailer with a chain saw and other fencing tools and metal posts. One side of the gully i near ground level and the other side has a 10 foot drop off

Well, if you use wood, use pressure treated. If you can afford it, use redwood.
Think of it as a 10ft by 11ft deck. Use treated wood. There are book tables that show what size joist to use to span a given length (check Menards or equiv). Otherwise I think 2 x 10’s spaced 16 inch on center to go across the brook would do. (2 x 12’s would be stronger). You might be able to get by with 1 inch lumber for the deck but I think I would use 2 inch. ***** this to the joists with galvanized screws or use galv. nails. I think I would rest this bridge on something solid on both sides of the brook; maybe cement blocks or ??. It wouldn’t hurt to build up some kind of side-guard down both sides so you don’t inadvertently drive off.
I’ve seen it done with old telephone poles and 2X6’s the bridge is now 20 years old and still strong. I don’t know where you would find the poles though.