Section 22350 of the Vehicle Code prohibits drivers from travelling " at a speed greater than is reasonable or prudent" under all the circumstances of the moment, including road conditions, weather conditions and traffic conditions. The roadside signs are prima facie speed limits, or speeds that are presumed to be reasonable and prudent for that type of roadway, from 70 mph on a highway to 15 mph in an alley.
Public roadways in Kern County can be roughly grouped into four categories, and each category has its own initial speed limit presumption:
Following the initial presumption, the government uses traffic surveys to study traffic patterns and engineering surveys to study typical road conditions in Kern County. The prima facie speed limit takes all this information into account, and may be reconsidered if the law changes, the road conditions change or traffic patterns permanently change.
Even if all of these surveys are done and the speed limit is set according to law, under Vehicle Code 22350 still says that it's the current "reasonable speed" that matters under existing conditions. So if you are on a wide open road with great visibility and little traffic, the speed limit could be higher. Conversely, traffic, children playing, a less than ideal road service or visibility, and a lower speed than posted may be the law. Use good situational awareness, be open to all possibilities, and use your common sense while driving on California roads.