Opening scene?
The movie begins with Leadbelly swinging a sledge hammer to break huge boulder rocks, next to a solid rock cliff.
Now I've never been to Angola, but Louisiana is not like Arizona.
When you make a movie 100 miles south of Dallas you have to make do with the outdoor scenery that is there. http://www.imdb.com/title/tt0074781/locations
What made me laugh is just after the scene you described, there was one where a bunch of people, all blacks, were dancing to Irish jig music. Presumably, this scene is set in the 1920s. "Irish jig" may not be the correct term for it but it's got to be close. I am no expert on Louisiana in the 1920s but I have trouble believing that blacks danced to that kind of music by their own choice.