William Christenberry, who is 73, has been one of Washington's most important artists for something like 40 years, working as a painter, fine-art photographer, sculptor and installer of found things. But the best way back to the origins of all his varied work, and to the heart of what it means, is through a series of scrappy little snapshots that Christenberry made in the 1970s as he toured and contemplated Hale County, Ala., where his family is from.