From the UC Davis transportation site
http://www.taps.ucdavis.edu/bicycle/...cdcyclist.html

According the California Vehicle Code, every person riding a bicycle upon a street or highway has all the rights and responsibilities of the driver of a motor vehicle. On campus traffic regulations are strictly enforced . You may be cited for running stop signs, riding at an unsafe speed for conditions, riding on the wrong side of the road or on sidewalks, wearing headphones while riding, not having legal brakes, etc.

From the California DMV site
http://www.dmv.ca.gov/pubs/vctop/d12/vc27400.htm
Wearing of Headsets or Earplugs
27400. A person operating a motor vehicle or bicycle may not wear a headset covering, or earplugs in, both ears.