National Geographic : 1913 Jul
A BEAVER DAM (SEE PAGES 797-800) Photo byGeorge Shiras, 3rd This particular structure was 3oo feet long, extending in broken curves across the valley and with awall 5feet high and 4feet thick at the base. It was composed of brush and mud, with an unusually large number of heavy stones along the rim. During July, 1912, 35feet of the dam were blown up by dynamite in order to harvest a hay crop in the meadow above. In less than five days the beavers had completely re built the dam. In October, 1912, the author made the small break in the dam near the left bank, shown inthis picture, so that when the beaver was warned by the receding water it would investigate the cause and set off the flash. In daylight thepictures of water arewhite with dark shad ows and reflections, while in the night picture following, the water is black and the reflections white.