The meat...
I'm trying to get caught up on updates a bit so rather than splitting this into two updates, I've condensed it down to one. First, here is the track plan for the Cajon Pass section modeling from roughly CP Walker to Sullivan's Curve:
I'm using Rubbermaid shelf brackets for this part of the layout. These are 18" brackets and in testing they hold pretty solid out to about 22-24" and then you can run into sag issues. What I decided to do is mount the brackets and then screw in a piece of dimensional lumber on top:
On top of that will be a box frame attached with metal 90 degree brackets. The box frames attached to each other with connecting plates and in a few locations one of the box frame members is actually attached to a vertical pillar, wall or ceiling and when all tied together is very stout. I have one bracket in the middle of the Sullivan's Curve area (widest part of the layout) that I will brace with a 45 degree piece of wood underneath:
The farthest bracket will be supported by vertical connections to the ceiling via the backdrop which I'll get to in a minute. Overall I wanted to avoid having additional brackets under the layout if I can so storage is free and clear.
I temporarily laid up a 1" sheet of foam insulation board so I could visually sort out curves and easements and also plot the grades to get under the layout for the turnaround loop.
and looking the other direction:
Once i was happy with the curves and scenery/track ratio, I drew the centerlines on the foam and cut out roadbed templates so I could make sure things looked ok. This was an additional waste step for some, but I'm really trying to get an idea in my head of how all this will look. Part of it is driven by this fun exercise on compressing scenes:
It is roughly 1,800 feet across Sullivan's Curve (one of the sharper prototype mainline curves) in real life. In N scale that's slightly over 11 feet:
Compressed more than half that is still big:
So some realization that this is going to be tough to capture well is setting in, but fingers cross. I originally allocated about 48 inches to this space, but in the end it will be closer to 54" inches wide once I looked at curves and scenery placements. Smallest radius curve is 18" with the largest being 21". I prefer 21" or higher for passenger equipment, but I can't compromise the aisle much more at this point. Hope for the best. 
I attached one of the vertical supports to the ceiling and tied it into the bracket below and clamped up some loose masonite hardboard to see where my 8 foot sheet gets me:
And the view from the other side with a little visual:
So I attached another vertical support from the ceiling and started cutting and attaching hardboard panels:
On the layout side I installed blocks to hold the boards in alignment and provide more screw locations and 90 degree metal brackets on the bottom to hold the bottom of the hardboard in alignment with the wall.
and here is the overall view:
I'm waiting to finish the curved parts of the benchwork on the front so I can still work on the backdrop without the reach in being too difficult. Here is the view in the other direction:
Roadbed and track next...
