I was trying to find out how they measured their distances but was unable to find any, yet. i did come across this though:
626.95. (a) Any person who is in violation of paragraph (2) of
subdivision (a), or subdivision (b), of Section 417 , or Section
12025 or 12031,
upon the grounds of or within a playground, or a
public or private youth center during hours in which the facility is
open for business, classes, or school-related programs, or at any
time when minors are using the facility, knowing that he or she is on
or within those grounds, shall be punished by imprisonment in the
state prison for one, two, or three years, or in a county jail not
exceeding one year.
(b) State and local authorities are
encouraged to cause signs to
be posted around playgrounds and youth centers giving warning of
prohibition of the possession of firearms upon the grounds of or
within playgrounds or youth centers.
(c) For purposes of this section, the following definitions shall
apply:
(1) "Playground" means any park or recreational area specifically
designed to be used by children that has play equipment installed,
including public grounds designed for athletic activities such as
baseball, football, soccer, or basketball, or any similar facility
located on public or private school grounds, or on city or county
parks.
(2) "Youth center" means any public or private facility that is
used to host recreational or social activities for minors while
minors are present.