Actually, that SP rule book calls a red over green "Block signal green for diverging route" (Rule 283), which is a bit cumbersome, so on the we Coast Division called it "low green". The Western guys called it "green bottom". "Diverging clear" is a more modern name. What's the date of that WP rule book? That layout doesn't really resemble the Cal-P very much because it traverses wide open terrain which is comparatively flat.