Margaret Sanborn resided in Mill Valley, California, north of San Francisco near the Pacific Ocean. She died early in 2005 leaving a son, David R. Sanborn, and a daughter, Catherine.
Margaret Sanborn came to prominence in 1966 with the publication of Robert E. Lee: A Portrait [1807-1861], the first volume of her two volume biography of the Confederate general which won critical acclaim.
In an interview given in 1997 at the Library of Congress, Sanborn relates the story of how she came to be the writer of the final volume in the Rivers of America Series, The American, River of El Dorado.
In 2004 Sanborn received a Milley Award for contributions to the arts from the Mill Valley Art Commission.