I think it's safe to say, that the Grateful Dead introduced a lot of Rock fans to the music's Country, Folk and Blues roots. There is even a CD called "The Roots of the Grateful Dead", which contains some of the original source material.

"Deep Elem Blues" comes immediately to mind. It was first recorded in the 1930s, as a Country tune, but it was also a Blues. Elem St. was the Red Light District in Dallas, Texas, or was it Houston?

I, being originally into Folk music, until I heard the Dead, in 1968, actually went and looked up quite a few of the original recordings.