California rider law
Lane splitting (CVC § 21658.1) is legal. CHP's safety tips warn that the danger grows with the speed difference and overall speed.
Helmets (CVC § 27803): every rider and passenger must wear a DOT-compliant helmet.
Before a mountain ride
Check Caltrans for closures, since many canyon roads close for snow, rockslides and fire.
Expect sand and rocks in corners after storms, and cyclists and slow traffic around blind bends.
Tell someone your route. Many roads have no phone signal for miles.