Back in 2016 I took the Parkfield Grade south from CA 198 to the Monterey County line where it continued over the crest of the Diablo Range as the gravel Parkfield-Coalinga Road. Parkfield-Coalinga Road crosses a old truss bridge from 1915 before ending on the San Andreas Fault in the community of Parkfield. Mile-for-mile the Parkfield Grade/Parkfield Coalinga Road is probably one of the most interesting rural routes in Central California:
http://surewhynotnow.blogspot.com/2018/09/parkfield-gradeparkfield-coalinga-road.html
Took a visit out to Parkfield today by way of the Parkfield Grade and Parkfield-Coalinga Road:
https://flic.kr/s/aHsmLQQUxN
On the Fresno County side much of the Parkfield Grade has been repaved and is a huge improvement over the surface I drove in 2016. The gravel just over the Monterey County Line appears to have had fresh grading which made for a smooth ride even in the rain.
Back on the 7th I took a day trip back out to Parkfield out on the San Andreas Fault Line . I decided on taking the high road to Parkfield which took me from CA 198 in Warthan Canyon south on; the Parkfield Grade, Parkfield-Coalinga Road, and Cholame Road/Cholame Valley Road to CA 41/CA 46. The Parkfield Grade and Parkfield-Coalinga Road crest the Diablo Range on a road grade which essentially plows directly over the mountainside rather than following a natural pass. If you're looking for a quality series of back roads (which aren't entirely paved) with the payoff being a relic quaint relic community then the trip on the Parkfield Grade, Parkfield-Coalinga Road, and Cholame Road/Cholame Valley Road is probably what you're looking for.
https://www.gribblenation.org/2020/03/return-to-parkfield-parkfield-grade.html