California's "Basic Speed Law" says you must:

The "Basic Speed Law" states that you may never drive faster than is safe for current conditions. For example, if you drive at 45 mph in a 55 mph zone during a dense fog, even though you are below the posted limit, you may be cited for driving "too fast for conditions."

• Keep your speed close to that of other traffic.
• Never drive faster than is safe for current conditions.
• Always drive at the posted speed limit.