Cal. Sts. & High. Code § 31851

Any money received from the sale or lease of property not needed for parking places shall be placed in such fund as the board directs, and may be used for any purpose for which revenues from fees, charges, and rentals for the use of parking places of the district may be used, except the proceeds from the sale or lease of property acquired with the proceeds of an assessment shall not be applied as a credit upon any assessments except those levied for the acquisition of the property.