I was just looking in that excellent Signor book.
JS discusses tunnel proposals and there is a full page illustration, from the Examiner, of the best one. Although done by others,[ probly when John was 9 years old] that page shows a bird's eye view of the Tehachapis, the style that John has taken to the acme, and a profile thru the tunnels, giving rates of grade and portal elevations. ANd another thing, the route is pretty close to straight between the SJV and Castaic. The surface route between the tunnels corresponds to the crossing of San Andreas. No Pie in the Crack for those folks . The proposal portrayed was deemed by JS to be the best of several, prompted, if I recall the fine print, by the '52 quake, and was done by an actual educated person, unlike a somewhat contemporary proposal by an LA County supervisor to tunnel [LARGE bore] thru the San Gabriel Mtns to provide a way to exhaust LA smog into the desert.
So the prelim has been around for decades. It looks as if all the desires of Dread Tejon Ranch are even satisfied- invisibility except where convenient to the planned Mega City of Tejon can be served. Perhaps the folks at Parsons Brinckledick would be interested in doing the fill in.
Maybe an intrepid person on here can show the illustration at the nest CaCAHSR board meeting and ask somebody 'How about this?" and 'Why not"?
I didn't cite the page numbers- y'all folks will have too much fun looking at ALL the amazing things JS jammed into his book, so if you don't got it, get it.