Earlier quoted context omitted.
Mountain ranges didn't seem to be a problem for Japan's high speed rail network.
That's because they mostly avoided mountains on their high speed routes. The Tokaido and Sanyo Shinkansen mostly follow the coastline and the Tohoku Shinkansen mostly goes through a valley. There are lines that do bore through mountain ranges, but nothing to the extent of several hundred miles as would be required for a line through the California coastal range.
https://en.m.wikipedia.org/wiki/Ch%C5%AB%C5%8D_Shinkansen
"About 90% of the 286-kilometre (178 mi) line to Nagoya will be built underground or through tunnels"