Dr. Douglass made careful measurements of the growth rings in logs used as supporting beams in the Pueblo Bonito structures, and then was able to fit them into an unbroken sequence of tree rings extending back into the past from the present day. Thus he was able to establish the dates when many of the Pueblo Bonito beams had been cut from living forests. His monograph, Dating Pueblo Bonito and Other Ruins of the Southwest, appeared in 1935 as the first of several papers presenting the scientific results of the Pueblo Bonito expeditions.