California Code, Public Contract Code - PCC § 20145

(a) In counties containing a population of 6,000,000 or over, the board of supervisors may by ordinance authorize any county officer as is deemed appropriate to take or perform any or all acts or actions permitted or required of the board by this article, including the authority to adopt and advertise plans and specifications, award contracts, approve bonds, or order the change or alteration of contracts, with respect to original contracts which do not exceed the total amount of three hundred thirty thousand dollars ($330,000) or with respect to changes or alterations to original contracts entered into by the board where the changes or alterations do not exceed 10 percent of the amount of the original contract or three hundred thirty thousand dollars ($330,000), whichever is less.  The aggregate total amount of those changes or alterations to an original contract may not exceed 25 percent of the amount of the original contract.  Any authorization pursuant to this section shall include detailed procedures governing the county officer in the exercise of that authority.

(b) Nothing in this section shall be construed to remove the county's requirement to follow the applicable provisions of the Public Contract Code as it relates to the advertising of public works projects and award of public works contracts.