According to the negative sleeve, the photographs in this group were taken in 1931. Key features of these images were nonexistent in 1931. Penguins were not exhibited at the San Diego Zoo until 1933. Alpha the Robot did not appear in the states until late 1934 and was a special attraction in San Diego during the California Pacific International Exposition (1935-1936). Based on this, it is most likely that the images were taken about 1935 during the exposition.