216 ANIMAL LIFE IN TEE ¥0 SEMITE 



dams and houses. In 1915, near Snelling, beaver work was seen on cotton- 

 woods up to 2 feet in diameter, though stems and boles of much smaller 

 size are more often sought. 



One particular cottonwood 10 inches in diameter was seen east of 

 Snelling on which a beaver had been at work for some time. The tooth 

 marks showed that the beaver had turned its head sideways when cutting. 

 The chips lying on the ground below the notch in the tree were from 1 

 to 2 inches long, i/g to % inch wide, and Yiq inch thick. Each consisted 

 of two or more flakes, loosely joined, indicating that several bites had to 

 be taken before a chip was entirely severed. The cutting on this tree 

 was on the side away from the water, yet the tree when downed would 

 have fallen into the river. 



In the neighborhood of Snelling, both above and below the town, much 

 work of the beaver can be found along the Merced River and in the ponds 

 and sloughs which were formed there in past years when gold dredgers 

 were operating. On the Tuolumne River, also, within 3 miles below 

 Lagrange, the industry of the beavers is manifest. Most or all of the work 

 of the beaver is done under the cover of darkness, so that the activities 

 of the animal have to be inferred from evidence of a circumstantial nature ; 

 but such evidence is in this case vinmistakable. It consists of trees 

 upon which the animals are cutting or which they have cut down, pieces 

 of wood from which the bark has been peeled, refuge or nest holes in the 

 banks of sloughs, broad runways beneath the stream-side vegetation or up 

 over dikes, dams across the larger sloughs, and, lastly, houses in or on the 

 banks of the ponds formed by these dams. 



On January 9, 1915, two beaver dams near Snelling were examined 

 in detail by the senior author. The first dam was across a narrow and 

 shallow slough between a rock pile left by a dredger on the one side and 

 a river-cut bank on the other. The dam, though small, was perfect, and 

 was curved, with the convex side downstream. (See pi. 37&.) The bottom 

 of the pond just above the dam had been deepened by digging out rocks 

 and mud to contribute to the dam. The dimensions of the dam were as 

 follows: length along curve 121/^ feet (3.8 meters) ; radius of arc about 

 10 feet (3 meters) ; thickness of base at middle, 31 inches (0.78 meters); 

 total height on lower side 19^/2 inches (0.5 meter) ; depth of water just 

 inside dam, I514 inches (0.39 meter) ; rise in water level of pond due to 

 dam, 12 inches (0.3 meter). The dam consisted of two types of sticks, dead 

 drift, and freshly cut green willow, some with the bark gnawed off. The 

 pieces used were up to 2 inches (50 mm.) in diameter. Some freshly 

 peeled sections of young willow stems and twigs averaging a yard in length 

 were used. There were also whole untrimmed tops of willows, just as 

 cut off, on the adjacent margins of the slough within 100 yards of the 



