(Whenever there is a Bluegrass festival), Dad goes and takes along his banjo.
It is an adverbial clause, and it modifies the verb “goes”.
It’s adverbial rather than adjectival.
Ask yourself what information the clause provides for you about the sentence. It’s telling you WHEN dad GOES places with his banjo.
Adverb clause as it describes the verb.Source(s): I’m a whiz.