According to Mather scholar Beth Gates Warren, Mather and Weston entered into a photographic partnership in 1921, and approximately twelve doubly-signed images from this period, among them the present portrait of Sandburg, are extant. This was the only time Weston co-signed work with another photographer.
This photograph of Pulitzer Prize-winning poet and biographer, Carl Sandburg, was taken in March 1921 on Glendale’s Monte Sano Bridge. Sandburg, who was married to Edward Steichen’s sister Lillian, was in California on a lecture circuit and to interview Charlie Chaplin for the Chicago Daily News. Weston and Mather made at least two photographs of Sandburg, one of which was included in their joint exhibition at the San Francisco Camera Club in July of that year.
Ref.:
Beth Gates Warren, Margrethe Mather & Edward Weston: A Passionate Collaboration (Santa Barbara Museum of Art, 2001)
Beth Gates Warren, Artful Lives: Edward Weston, Margrethe Mather, and the Bohemians of Los Angeles (J. Paul Getty Trust, 2011)