BOB2 for president!
The CHSRA really, really didn't want to study Altamont / Dumbarton in any more detail than they had to. One of the advocacy groups, TRANSDEF, did it for them by hiring the French firm SETEC Ferroviaire (involved in design of the French HSR network).
Here is a map I made of it (with a Dumbarton tunnel, because been there done that)
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drive.google.com]
Here is a detailed report (no longer on the TRANSDEF website but thankfully still available in archive.org)
[
web.archive.org]
Using modern electric rolling stock this can be done with 4.5% ruling grades and even shorter tunnels.