California Code, Streets and Highways Code - SHC § 18190

The money collected by the tax collector shall be paid by him, as fast as collected, to the city treasurer, who shall place it in a special fund designated by the name of the improvement proceeding, and payment shall be made out of said special fund only for the purposes provided for in this part.  To expedite the making of any such improvement, the city council may at any time transfer into said special fund, out of any money in the general fund, such sums as it may deem necessary, and the sums so transferred shall be deemed a loan to such special fund, and shall be repaid out of the proceeds of the assessments provided for in this part.