Baja California vs Lower California

Baja California and Lower California both are nouns.

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

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

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

Other synonyms of Baja California include Baja California Peninsula.

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