Here is an excellent vid of Ry Cooder in the 1970's, doing Woody Guthrie's Viglilante Man, playing an expensive Martin guitar in Open D.:
https://www.youtube.com/watch?v=x4KmbUCwkyEPS, it's the same tuning he used in the Prodigal Son vid, except with the Prodigal Son vid the capo has the guitar playing several frets up. I think Ry uses Open D a lot.