REBUILDING A BEAVER COLONY 129 



boulder too large to be removed. At a dis- 

 tance of eighty-one feet from the lower end 

 the canal-builders came in contact with granite 

 rock and brought the canal to a stop by en- 

 larging the upper end into a basin about ten 

 feet across. 



The entire length of this canal was through 

 the sediment of a former beaver pond. After 

 making a pond beavers must occasionally raise 

 the height of the dam to deepen the water, 

 and also dredge the mud from the bottom. But 

 despite both dredging and dam raising, the 

 pond sooner or later fills with sediment and 

 has to be abandoned. In due time it is over- 

 grown with grass or a forest. 



Food shortage complete exhaustion of the 

 aspen growth had compelled the abandon- 

 ment of the Meadow Colony after it had been 

 a beaver settlement for a great many genera- 

 tions. Two large ponds, a dozen smaller ones, 

 and three houses were left to their fate. Most 

 of the smaller ponds were completely lost, being 

 overgrown with willows. Two of the houses 

 had crumbled and were now low wild flower 

 beds. 



Since abandonment a number of aspen groves 

 had grown, and although these were some dis- 

 tance from the stream, they could be reached 

 and would furnish necessary food supply. 



