Garcia/Dylan question

[Jason Chastain]

This is from a Dylan show (11-16-80, before "To Ramona"): Bob: "Why, I don't know exactly what to say here. Different people have been coming down to the theater every night so far, and this night is no exception, I guess. Anyways, (laughs) keep...uh...um...this is a young man, I know you know who he is, uh, I played with him a few times before - I'm a great admirer and fan of his, and support his group all the way...Jerry Garcia. He's gonna play with us, uh...key of C"   My question: When did Dylan & Garcia play together before 1980?   Deadbase lists 1988 as the first time Dylan sat in with the Dead. Any ideas?   Thanks, Jason