CMOS 16 CHANGES, #8
The 15th edition of The Chicago Manual of Style said that “Southern California” should have both words capitalized, but “northern California” should not. This has changed in the 16th edition.
CMOS-16 rule 8.46 says that both Southern California and Northern California are capitalized. This is not the case for any other states.
Also capitalize in these instances:
the North, Northern, Northerner (and the South, Southern, and Southerner) in American Civil War contexts
the Deep South
the South of France (region)
Southeast Asia
North/South Africa, North/South African countries
North/South America, the North/South American continent
the North/South Atlantic
the Northern/Southern hemisphere
Lowercase in these instances:
northern/southern (part of a country)
a northerner/southerner (outside of Civil War contexts)
in northern/southern Africa
a northern/southern Atlantic route
north/south, northern/southern, northward/southward, to the north/south (directions)