> The area around the "pinnacles" was noted as the big challenge, if they wanted a line to go this way via Hollister.

The Pinnacles are the northern half of a geological formation somewhere down around the Grapevine, not sure exactly where, and that projected route through Tes Pinos, Pacines, etc. runs almost on top of the San Andreas fault. The quarry at Logan is a piece of the Sierra Nevada granite which has been brought north along the fault by the Pacific Plate. Shake, Mamma, Shake. Parkfield isn't all that far off this route either.