The original War Department 1853 "southern pacific" route survey would have gone straight down the Valley created by the San Andrea fault and crossed over around Coalinga, IIRC.

Back in the 90's I was asked to look at a proposal the "extend" I-40 west from Barstow, via Bakersfield (federalizing SR-58).?)tending all of the way to somewhere between Camp Roberts and Paso Robles and up 101 to San Jose (where it logically should have ended...?). This route had very good grades and relatively easy engineering (especially compared to Pacheco Pass...?) and could easily have handled a RR.

The desire to connect to the traffic coming down to the Valley from the Southern gold fields, the low cost to construct, and the ability to drive the line quickly to the Tehachapi Pass and head off any other "potential" competing line coming west on the National Road route, maybe one coming via Needles, from using it to enter CA was why the original route was dropped. And, once they'd reached Tehachapi, SP would get the Cerro Gordo traffic, before the Los Angeles and Independence could build through Cajon Pass, and up to the "big strikes" at Cerro Gordo and Bodie, where it would meet up with the then still to be financed, but yet, later actually built, "Carson and Colorado" RR. All of which was being paid for by the "Silver Kings", who were financing this western narrow gauge "empire" that they hoped would end the big four's predatory monopoly in the west.

The politics, financial games, and RR schemes for the RR's in this period in CA are still all around us, if we look carefully. Foe example, like every day, when 50,000 folks ride over the Los Angeles and Independence's former narrow gauge mainline from the Santa Monica Pier, through Palms, and over to USC.