CA Gov't Code Section 31000.9

In counties containing a population of 6,000,000 or over, the board of supervisors may, by ordinance, authorize county officers having responsibility for the design and construction of county projects to enter into contracts for architectural, engineering, and related services where the amount of the contract does not exceed seventy-five thousand dollars ($75,000), and to enter into amendments to those contracts entered into by the board where the amount of any amendment does not exceed 10 percent of the amount of the original contract or seventy-five thousand dollars ($75,000), whichever is less. The aggregate total amount of the amendments to an original contract may not exceed 25 percent of the amount of the original contract. Any authorization shall include detailed procedures governing the county officer in the exercise of that authority.