California Code, Vehicle Code - VEH § 40521

(a) Except when personal appearance is required by the bail schedule established under Section 1269b of the Penal Code, a person to whom a notice to appear has been issued under Section 40500, who intends to forfeit bail and to pay any assessment may forward by United States mail the full amount fixed as bail, together with the appropriate amount of any assessment, to the person authorized to receive a deposit of bail.  The amounts may be paid in the form of a personal check which meets the criteria established pursuant to subdivision (c) of Section 40510, or a bank cashier's check or a money order.  Bail and any assessment shall be paid not later than the day of appearance set forth in the notice to appear or prior to the expiration of any lawful continuance of that date.

(b) Bail forwarded by mail is effective only when the funds are actually received.

(c) Paragraph (1) of subdivision (a) of Section 40512 is applicable to bail paid pursuant to this section.  Upon the making of the order pursuant to Section 40512 that no further proceedings be had, the amount paid as bail shall be paid into the city or county treasury, as the case may be, and the assessment shall be transmitted to the State Treasury in the manner provided in Section 1464 of the Penal Code.