Written by Robert Hunter and Bob Weir, "Sugar Magnolia" is one of the most well-known songs by the most obscurely famous band. First performed at the Fillmore West in San Francisco, in June of 1970, Deadheads will be quick to point out that "Sugar Magnolia" is the band's second-most-frequently-performed song, trailing only behind "Me & My Uncle."
The line "jump like a Willys in four wheel drive" refers to the model of jeep manufactured by Willys-Overland Motors, most likely the Willys MB, which saw the most production of the Willys line at over 335,000 produced for WWII. An article on the Willy jeep, complete with its jumping ability, appears in the November 1992 issue of Smithsonian magazine.
Frequently in live performances, this song is divided into two parts, with the coda coming long after the song proper. That delay might be a few drum beats, a few songs, or a few days, depending, as everything does, upon the mood of the band.
A typical literary reference is the similarity between the girl described in this song and the character Goldberry in J.R.R Tolkien's Fellowship of the Ring - right down to being down by the river and rolling in the rushes.