Sonoma County has fairly good bus services. You can see their transit network here: https://sctransit.com/ .

Amtrak has stops in Oakland, Berkeley and Richmond. From Richmond, you can take a Golden Gate Transit bus (https://www.goldengate.org/assets/1/...bayol.pdf?7559) to San Rafael.. From San Rafael, you can take a bus to Santa Rosa (https://www.goldengate.org/bus/route...co-101-update/). From there, another bus to Guerneville, Monte Rio, or Sebastopol. It will take some planning and likely some local transportation to get from the train to bus station. I would guess that you can take the bus from either Oakland or Berkeley, as well.

Note that while Amtrak from Southern California doesn't go directly to San Francisco, you can take a separate line from San Jose to San Francisco and from SF you can get buses directly to Santa Rosa. In reality, that might be your most direct route.

As for the Western Express, be aware that the climb over the Sierra (Carson Pass) is no joke. You will have to be prepared to climb over the 8574 foot pass in the first part of your trip. With 50 mile days, it is 2 days from Guerneville to San Francisco (I overnighted in Petaluma). If you'd like an idea of what the ride from SF to Carson City on the Western Express is like, check out my journal.

Good luck and keep us informed of your progress.

By the way, congratulations on your retirement!