Cal. Public Contract Code - PCC § 20103.8. Section 20103.8.
A local agency may require a bid for a public works contract to include prices for items that may be added to, or deducted from, the scope of work in the contract for which the bid is being submitted. Whenever additive or deductive items are included in a bid, the bid solicitation shall specify which one of the following methods will be used to determine the lowest bid. In the absence of a specification, only the method provided by subdivision (a) will be used:
(a)
The lowest bid shall be the lowest bid price on the base contract without consideration of the prices on the additive or deductive items.
(b)
The lowest bid shall be the lowest total of the bid prices on the base contract and those additive or deductive items that were specifically identified in the bid solicitation as being used for the purpose of determining the lowest bid price.
(c)
The lowest bid shall be the lowest total of the bid prices on the base contract and those additive or deductive items that when taken in order from a specifically identified list of those items in the solicitation, and added to, or subtracted from, the base contract, are less than, or equal to, a funding amount publicly disclosed by the local agency before the first bid is opened.
(d)
The lowest bid shall be determined in a manner that prevents any information that would identify any of the bidders or proposed subcontractors or suppliers from being revealed to the public entity before the ranking of all bidders from lowest to highest has been determined.
A responsible bidder who submitted the lowest bid as determined by this section shall be awarded the contract, if it is awarded. This section does not preclude the local agency from adding to or deducting from the contract any of the additive or deductive items after the lowest responsible bidder has been determined.
(e)
Nothing in this section shall preclude the prequalification of subcontractors.