I had a look at the backstory of CA 284 and CA 285 as a Paper Highways article. CA 284 and CA 285 were both adopted as part of 1970 Legislative Chapter 1473 in the Sierra Nevada Mountains of Plumas County. Legislative Chapter 1473 highway adoptions appear to have been contingent on the Division of Highways/Caltrans taking over roadways built to State standards. CA 284 on Frenchman Lake Road was apparently easily adopted into the State Highway system whereas CA 285 on West Street and Lake Davis Road had drainage issues. CA 285 was ultimately never became a reality and was deleted from the State Highway System in 1998.
https://www.gribblenation.org/2020/05/paper-highways-california-state-route.html