I found this fascinating quote today:
The Grateful Dead’s musical influences varied widely; in concert recordings or on record albums one can hear psychedelic rock, blues, rock and roll, country-western, bluegrass, country-rock, and improvisational jazz. These various influences were distilled into a diverse and psychedelic whole that made the Grateful Dead “the pioneering Godfathers of the jam band world.”[ 7 ] New Release : Winterland 1973: The Complete Recordings Artist: The Grateful Dead (read more)New Release : To Terrapin: May 28, 1977 Hartford, CT Artist: The Grateful Dead (read more)New Release : Dick's Picks Volume 15: Englishtown, NJ, September 3, 1977 Artist: The Grateful Dead (read more)New Release : Dick's Picks Volume 5: Oakland Auditorium Arena, 12/26/79 Artist: The Grateful Dead (read more)New Release : Dick's Picks Volume 28: Pershing Municipal Auditorium, Lincoln, NE, 2/26/73 & Salt Palace, Salt Lake City, UT, 2/28/73 Artist: The Grateful Dead (read more)New Release : The Closing Of Winterland: December 31, 1978 Artist: The Grateful Dead (read more)Listen to track: Sugar Magnolia (Remastered Version) Album: American Beauty Track: Sugar Magnolia (Remastered Version) View The Grateful Dead's page on Rhapsody (read more)Listen to track: Casey Jones Album: Workingman's Dead Track: Casey Jones View The Grateful Dead's page on Rhapsody (read more)Listen to track: Uncle John's Band (Remastered Version) Album: Workingman's Dead Track: Uncle John's Band (Remastered Version) View The Grateful Dead's page on Rhapsody (read more)Listen to track: Truckin' (Remastered Version) Album: American Beauty Track: Truckin' (Remastered Version) View The Grateful Dead's page on Rhapsody (read more)Listen to track: New Speedway Boogie Album: Workingman's Dead Track: New Speedway Boogie View The Grateful Dead's page on Rhapsody (read more)Grateful Dead, May 1977
You should read the whole article.