This article is from the California Driving (and Surviving) FAQ, by "George J Wu" email@example.com with numerous contributions by others.
from firstname.lastname@example.org (David Cortesi) on 15 Jun 93:
Bicyclists are "vehicle operators" in almost every sense under the vehicle
code. They are not restricted to particular lanes or parts of the road,
except that when passing another vehicle, preparing for a left turn, or to
avoid unsafe conditions, they should ride as far to the right "as
practicable" [CVC 21202(a)]. On a section of highway that carries traffic
in one direction only and has two or more marked traffic lanes, bicyclists
may ride as near to the left as practicable [CVC 21202(b)]. They are also
subject to the law on two-lane highways that slow traffic must pull over,
wherever sufficient area for a safe turnout exists, when 5 or more vehicles
are behind it and where passing is unsafe [CVC 21656].
So if the cyclist was riding as far to the right as practicable for the road
surface conditions and holding up less than 5 vehicles, he or she is within
the law, and motorists are responsible for passing the cyclist in a way that
is safe for all.