California black oak vs oak

California black oak and oak both are nouns.

Word	Noun	Adjective	Verb	Adverb
California black oak	Yes	No	No	No
oak	Yes	No	No	No

As nouns, oak is a hypernym of California black oak; that is, oak is a word with a broader meaning than California black oak:

California black oak: large deciduous tree of the Pacific coast having deeply parted bristle-tipped leaves
oak: a deciduous tree of the genus Quercus; has acorns and lobed leaves

Other hypernyms of California black oak include oak tree.

California black oak (noun)	oak (noun)
large deciduous tree of the Pacific coast having deeply parted bristle-tipped leaves	a deciduous tree of the genus Quercus; has acorns and lobed leaves
	the hard durable wood of any oak; used especially for furniture and flooring