Apparently California uses something called "Speed Zone Surveys" to determine speed limits, and if a jurisdiction has a posted speed limit which is lower than that in the "Speed Zone Survey", then speeding tickets can be dismissed if contested. IIRC, a rather vocal Ridgecrest resident used this defense for a ticket issued to his wife by the R/C police, and was successful. I believe that city changed the posted limit on the section of the street in question to reflect the results of a Caltrans "Speed Zone Survey".
This might account for why there are wide differences in posted limits in various towns - 55mph in Olancha, 25mph in Independence, etc.
It will be interesting to see if the speed limit between the Sidewalk to Nowhere and Mazurka Canyon Road remains at 25.