San Gimignano & Volterra in One Day from Siena via Public Transit?

We did a recent tour with Road Scholar and each of those towns were half day visits, so you might be able to do them in one full day if you got an early start.
We stayed in Siena and had a bus take our group tour.
Don't know anything about public transport, but I know the bus transport from Florence to Siena was so confusing, I gave up and took the 1.5 hr train instead.

Thanks. I know a tour is an option but would like to avoid that if I can. I want to be able to take my time and see what I want to see on my schedule.

I will be traveling solo, too, so, I have a higher premium for such things traveling solo.

As a comparison, since you're from CA, think of touring wine country in Healdsburg or Sonoma by public transportation. Everything is so spread out. We just returned from Siena, and gave up on public transportation, as there were so few public bus routes and times. We instead booked a small group tour, which used a van. Without a car, it's just a challenge, and my husband was adamant that he was not driving.
Wishing you a great trip!

Thanks, Pat. That perspective and distance comparison is helpful.

I may just plan on having 4 nights in Siena and do a day trip to both cities, each. I will consider a day tour that covers both, should I find one that is more of the "drop off" variety rather than a guided deal.

I am not willing to drive. If I was with another person I would, but do not care to incur that expense (and sometimes hassle) solo!

https://get-tours.it
https://www.tripadvisor.com/Attractions-g187894-Activities-c42-Cortona_Province_of_Arezzo_Tuscany.html

I would recommend you plan on separate trips. There is a bus from Siena-Via Tozza (130) that goes to San Gimignano. To go to Volterra you will have to do a bus transfer in Colle V. Elsa. We have made this trip, and it took about 2 hours from Siena to Volterra. Looking at the bus schedule from Volterra to San Gimignano, or reverse, you are correct the schedules do not align well.