CAL. RTC. CODE § 11911 : California Code - Section 11911

(a) The board of supervisors of any county or city and county, by an ordinance adopted pursuant to this part, may impose, on each deed, instrument, or writing by which any lands, tenements, or other realty sold within the county shall be granted, assigned, transferred, or otherwise conveyed to, or vested in, the purchaser or purchasers, or any other person or persons, by his or their direction, when the consideration or value of the interest or property conveyed (exclusive of the value of any lien or encumbrance remaining thereon at the time of sale) exceeds one hundred dollars ($100) a tax at the rate of fifty-five cents ($0.55) for each five hundred dollars ($500) or fractional part thereof.

(b) The legislative body of any city which is within a county which has imposed a tax pursuant to subdivision (a) may, by an ordinance adopted pursuant to this part, impose, on each deed, instrument, or writing by which any lands, tenements, or other realty sold within the city shall be granted, assigned, transferred, or otherwise conveyed to, or vested in, the purchaser or purchasers, or any other person or persons, by his or their direction, when the consideration or value of the interest or property conveyed (exclusive of the value of any lien or encumbrance remaining thereon at the time of sale) exceeds one hundred dollars ($100), a tax at the rate of one-half the amount specified in subdivision (a) for each five hundred dollars ($500) or fractional part thereof.

(c) A credit shall be allowed against the tax imposed by a county ordinance pursuant to subdivision (a) for the amount of any tax due to any city by reason of an ordinance adopted pursuant to subdivision (b). No credit shall be allowed against any county tax for a city tax which is not in conformity with this part.