46 THE BEAVER 
While no beavers were there at the time of the examination 
the work looked fresh, and certainly had been done within a 
year. The visit was made in early autumn and the tunnel 
had been worked the preceding fall. The nearest stream is 
four or five miles away and that not suitable for beavers. 
On Carnelian Creek in Yellowstone Park the beavers had 
done an interesting piece of engineering. On the flat on the 
left bank was a series of four good-sized ponds, which re- 
ceived their water supply from the creek in the following 
manner: An old dam, or its remains, extended part way 
across the stream, which was quite wide at this point, and 
which also made a considerable bend; from the end of this 
old dam an extension had been carried part way to the 
right bank in such a manner as to divert a portion of the 
stream into the upper pond, whence of course it went on 
down through the others. The creek had so much fall that 
the last of the ponds was several feet above its level (Fig. 18). 
At times beavers drain the water from their ponds, either 
partially or entirely. Why,I donot know. Mills expressed 
the opinion that it might be for sanitary reasons, to permit 
the sun and air to purify the bottom of the pond and interior 
of the lodge, if one was present. Later the pond would be 
filled again by closing the opening in the dam. I know of 
one pond which was full in February, empty the following 
October (no visit made between those dates), and full again 
in November. 
In the Yellowstone a pond with two good-sized lodges had 
been drained by a hole through the dam at the stream chan- 
nel. The pond bottom was full of devious channels which, 
presumably, the former occupants had dug. The pond 
was apparently abandoned because all the aspens on either 
side had been harvested. The beavers were living in another 
pond a short distance upstream, and possibly in another 
below (Figs. 19 and 20). 
