Paul Simon’s Riddle?

Paul Simon’s Riddle?

I am sure that Paul Simon did not intend a riddle with the first line to “Graceland“:
“The Mississippi Delta was shining like a National guitar.”
What is the meaning of the image? Is it poetry? Metaphor? What?

I have been trying to figure out the riddle since I first heard the song, probably at Paul’s “Concert in the Park”, 1991, I think, part of the “Rhythm of the Saints” tour. I have posed this question to a number of people, including several musicians. No one had the answer. Only one person got it right. He attributed his success to his experience with crossword puzzles.

Hint: the answer is in the plain text.

When I finally figured it out, it came in a blinding flash.

You can come up with the answer if you watch the Traveling Wilburys’ video for The Wilbury Twist. Hint: focus in on Tom Petty.

I would love to see some results in Comments.