Show history from trees tree for a quarter of a century dr douglass of the university of arizona has studied the rings which mark the annual growth of trees he demonstrated that the rings formed each year vary in width in direct proportion to the amount of rainfall a wet year produces a thick ring and vice versa tree growths in the giant sequoias of california were traced back three thousand years doctor douglass made an unbroken annual calendar back to A D by the study of timbers taken from pueblos he be gave exact dates of events in the history of those indian peoples back as aa far as the eighth century |