Were The Grateful Dead a jazz band?
Phil Lesh (Grateful Dead bass guitarist) talks about the influences of Miles Davis and John Coltrane:
"The basic inspiration for The Grateful Dead was the Miles Davis Quartet with Coltrane or Trane's quartet from the early Sixties. So that was pretty much the inspiration for the way we approach our music."
Miles Davis on Jerry Garcia:
So it was through Bill Graham that I met the Grateful Dead. Jerry Garcia, their guitar player, and I hit it off great, talking about music - what they liked and what I liked - and I think we all learned something, grew some. Jerry Garcia loved jazz, and I found out that he loved my music and had been listening to it for a long time. He loved other jazz musicians, too, like Ornette Coleman and Bill Evans.”
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LuckyCharms: I've always heard The Grateful dead as predominantly a jazz band, with rock, R&B, folk, classical, Motown and bluegrass influences.
Below is some audio I found which displays pretty much all of these styles rolled into one band, and I don't believe there will be another musical collaboration like the Grateful Dead ever again.
This is a compilation of the Grateful Dead playing various iterations of "Feeling Groovy" and "Tighten Up" from the late 60s and early 70s. Some amazing and musically complicated interpretations in here...something nice to put on and give a good listen to as you try to discern each individual instrument. I hear a lot of Miles Davis and John Coltrane influenced themes in here...not directly, but stylistically.
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along with Pink Floyd, Allman Bros, Santana, etc
A friend put it beautifully: 45 seconds of really interesting stuff, followed by 45 minutes of boredom. 
a little bit of country in there too. And although my husband (wrongly 
) called it disco, Shakedown Street was definitely funk.
Grateful Dead music to my ear is music with a heavy influence from Louisiana music genre styles.
This is a note for note recreation of a Grateful Dead jam by Holly Bowling.
This jam was not rehearsed by the Dead...it was played by the Dead only one time, and never again recreated by them. There was no sheet music for this...it was not a composed piece of music. Knowing this...I call this jazz music...unplanned, complex, and completely improvised, and you can really hear it when played by others on an instrument other than guitars.
That the Dead aimlessly noodled is a myth, except during the "space" segment of their shows, where the "noodling" was expected and purposeful. The space segment of their shows were an experiment to see where they could take sound...
That was Phil Lesh who said that quote, not Bob Weir.