The route begins at
SR 113 in
Knights Landing in
Yolo County. It then heads northward and enters
Colusa County, where it has a short overlap with
SR 20. It then enters
Glenn County, where it overlaps
SR 162 through the cities of
Codora and
Glenn. It then continues northward to its end at
SR 32 in
Hamilton City. SR 45 is part of the
California Freeway and Expressway System, but is not part of the
National Highway System, a network of highways that are considered essential to the country's economy, defense, and mobility by the
Federal Highway Administration. ==Major intersections==