Cal. Gov. Code § 43771

The legislative body of any city shall keep the funds arising from the sale of bonds pursuant to this article separate and distinct from all other municipal funds in a fund to be called “general improvement fund,” and shall invest and reinvest the money in bonds issued by the city, or bonds issued for street, sewer, drainage, or any other improvements within the city. It shall collect the principal of and interest on such bonds and credit it to the fund.