Lower California vs Baja California

Lower California and Baja California both are nouns.

Word	Noun	Adjective	Verb	Adverb
Lower California	Yes	No	No	No
Baja California	Yes	No	No	No

As nouns, Lower California and Baja California are synonyms defined as:

Lower California and Baja California: a mountainous peninsula on northwest Mexico

Other synonyms of Lower California include Baja California Peninsula.

Lower California (noun)	Baja California (noun)
a mountainous peninsula on northwest Mexico	a mountainous peninsula on northwest Mexico