I took a look into the backstory of CA 175. CA 175 exists in two segments; Hopland east to Lake Port was part of Legislative Route 16 whereas Lake Port to Middletown was part of CA 29 before the 1964 Highway Renumbering. CA 175 is an extremely curvy highway and the portion between Lake Port west to Hopland is a good representation of a 1909 First State Highway Bond Act grade.
https://www.gribblenation.org/2020/09/california-state-route-175.html