The Surf Line between L.A. and San Diego originally built by the Santa Fe, but now owned by Amtrak has a bunch of very low wooden trestles over marsh land. If you want any sort of high bridge, the only way to get it is to either raise the track or lower the benchwork. Whatever height you want the briodge to be over the benchwork, the track has to be at the same distance from the benchwork. What you can do to lower the bench work is to do what hot rodders have done for years to lower their cars. It is what is called a "Z'd" frame. Essentially you take a 1 x 4, or a 1 x 3 going down from the bench workwhere you want your gorge to start. Make the board long enough to put the top of the new bench work at the bottom of your gorge. Then you fasten a second 1 x 3 or 4 parrallel to the existing benchwork at the end of the board you just bolted to the benchwork. Finally fasten a second 1 x 3 or 4 from the other end of the new lower piece back up to the original bench at the other end of your gorge. Finally, cut out the piece of original framework that is bridging your new gorge.
