SOME INTERESTING BEAVER DAMS IN COLORADO 433 



was stored in this pond, though many sticks peeled of their 

 bark were lying in the water showing that beavers had been 

 feeding there. 



Some 170 feet above the dam a slough 15 feet wide enters 

 the pond from the southwest. Across this, 100 feet back from 

 the river, is a ver}' substantial dam, 20 feet long and 8 feet 

 wide, apparently constructed ver}'- largely of mud (PI. xxviii, 

 fig. 2) ; it also appears to be an old construction, though some 

 new work had lately been done on it. Then 130 feet above is 

 another across the same slough. This is new work, and ex- 

 tends 50 feet west of the slough to cut off the overflow there, 

 and then turns and by a series running from hummock to hum- 

 mock crosses another smaller slough which flows northwest. 



Also, as the map shows (pi. xxvi) its course is southeast and 

 then southwest until it connects with a dam made many years 

 ago and now all overgrown with grass. This old dam crosses 

 the slough to the west of the. junction with the new, but that 

 part the animals did not use. But they did use the part running 

 off to the southeast, patching it wherever necessary. West of 

 this dam is another old one not now used, discernible as a 

 grassy line hardly raised above the surrounding level. 



The other 2 long dams to the west are constructed in much 

 the same manner as the preceding, as well as the shorter ones, 

 and much land was flooded by them. 



It seems rather difficult to understand fully the object of all 

 these ponds and dams, for there is only i other house besides 

 the 2 already mentioned, and the land is so flat and level that 

 the beavers would have to tunnel a very long distance before 

 the end of the burrow would be in dry ground, as even outside 

 the flooded land the surface rises so little that the water level is 

 only a short distance underneath. Probably the main idea was 

 to give the inhabitants territory with deep water about which 

 they might move under the ice and snow during the long win- 

 ter. But this theory does not account for such a large flooded 

 district, as I doubt if, outside the sloughs and ditches, there was 

 very much water deep enough for a beaver to swim in under the 

 ice. There were plenty of muskrats about the place who could 

 use it, however. It may be that the beaver, having no way of 



