No pictures this post. I set up the laser level and checked my proposed route down the other side of the creek from the lower switchback turnout switch across Cox Creek and around the basin on the eastern side of Cox Creek. This works well as the south side (hill) of the basin lines up with the south side (hill) below the upper switchback tracks. The real trick is crossing the side creek which forms this basin. It's a broad flood plain where the tracks cross it - about 15 feet across. This will work fine as the old bridge sections that Fred is giving the RGS are shorter sections and rest on smaller stringers. I will have to excavate the channel between the bridge piers but that should not be too bad as the dirt will be used as fill nearby.
This survey did allow me to get the lay of the land and plug the numbers in a big spreadsheet which allows me to plug in proposed gradient to see how it lines up with the actual terrain. The trick is to have about the same amount to fill as cut so all the dirt can be reused. And the ideal plan is to cut out any digging not necessary. However, in this section of the railroad, we are trying to go downhill as "fast as possible" which means an average of 2.5%. Using the spreadsheet I determined the first 10 feet of track from the switchback switch will be the pitch over track from 0% (level) to 1.25%. The next section which is actually on the bridge will pitch over from 1.25% to the 2.5% grade. This grade will be maintained all the way down to the side creek crossing where it crosses on a long, yet low, bridge (about 15 long overall - really depends upon how long those bridge sections I will be reusing are...) The tracks then will go into a cut into the hill as it curves around to line up with the big bridge crossing back over Cox Creek.
The upper bridge (Bridge 2B) appears to be 55' long and about 5' high at the creek (to the top of the deck.) The middle bridge (Bridge 2C) appears like it will be 15' long and about 12" high over the creek. (Plenty of space under it to allow water to flow.) The big bridge (Bridge 2D) is still not completely surveyed. Since I have to do this at dusk when I can see the laser, I had only enough time to do the first 200 feet of this track. 200 feet is 5 feet short of where the tracks cross back over on the big bridge. The eastern abutment of the bridge should be about 160' track feet from the lower switchback switch. By the time it crosses the creek, it appears to be about 8 and a half feet tall.