California Code, Streets and Highways Code - SHC § 2150

All amounts paid to each county, out of the Highway Users Tax Fund shall be deposited in its road fund.  The board may deposit in said fund any other money available for roads.  All money received by a county from the Highway Users Tax Fund and all money deposited by a county in its road fund shall be expended by the county exclusively for county roads for the purposes specified in Section 2101 or for other public street and highway purposes as provided by law.

The amounts paid to a county for snow removal on county roads and for heavy rainfall and storm damage on county roads, pursuant to Section 2110, shall be kept in separate accounts in its road fund and shall be used solely for the purpose for which apportioned.