If I found that in the area you say, and there is no evidence of human-made slag or other refuse such as would be made by an industrial incinerator of sorts, I would assume it was a tektite. Tektites are produced in massive quantities as a result of large fiery meteors impacting the earth. They are just melted sand - essentially a natural form of glass. In either case you either have a man-made type of glass or a space-made type of glass. I would go with the space-made theory.