Southern California, and all of California, are in both the Northern and Western Hemispheres.
The hemisphere that is south of California is the Southern Hemisphere.
Northern hemsphere
Antarctica and Australia.
The Southern Hemisphere is south of California.
California is in the northern hemisphere, as it is North of the Equator. And is in the Western Hemisphere, as it is to the West of the Prime Meridian.
To make a long story short, yes.
California is located in the northern hemisphere.
South of the northern hemisphere is the southern hemisphere. There is no hemisphere "south of the western hemisphere" which extends to the South Pole. (East or west of the western is the eastern hemisphere.)
Baja California is in the Western Hemisphere.
the hemisphere south of Oklahoma is the southern hemisphere
Baja California is in the Western Hemisphere.
California is in the northern hemisphere :P