1080 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [2] 



unknown depth, completely saturated with water, would in this way 

 flow down into the gulch beneath.* 



The efl'ect on the creeks into which this enormous mass of earth de- 

 scends is indescribable. 



The first result is that the creek is completely dammed up by the av- 

 alanche. Now, if this were a dam of dry earth the creek would rise till 

 it overflowed the crest of the dam, and then, cutting a channel over the 

 top, it would finally wear a gap down through the dam to its own natural 

 level. But in this case, instead of being dry earth, the dam is almost 

 mud, and the water above it as it rises pushes this saturated mass before 

 it instead of waiting to rise up over it, and mingles with it, the whole 

 commingled mass then flowing down through the caiion to the river 

 below. 



What has just been described as happening to creeks generally when 

 land-slides occur from an excessive rainfall is what actually occurred in 

 the stream on which the United States trout ponds are built. The con- 

 sequences to the ponds were terrible. The trout-pond station was built 

 so far above the McCloud that the river could not reach it. It was also 

 so guarded from high water in the creek that the floods could not reach 

 it in that direction. But for this invasion of mud no provision had been 

 made. It had not even been dreamed of, nor did the possibility of its 

 occurring ever enter any one's mind until it came. 



As the mass of mud rolled down the creek towards the ponds nothing 

 could be done but to let it come into the ponds, because to shut ofl" the 

 mud would also shut off the water-supply from the trout, which would 

 soon be fatal. On it came, increasing in volume till it began to fill 

 the upper trout pond. In a very short time this poud was filled nearly 

 to the top with mud, and then the men had to get into the pond and 

 shovel out the mud. By the time this pond was excavated it was time 



* These laud-slides furnished a rude and rather novel method of determiniug what 

 could be discovered iu no other way, namely, the intervals at which great rains have 

 fallen in past generations. It is as follows: The size of these land-avalanches corre- 

 sponds very considerably with the amount of rainfall at the time the slide occurred. 

 The greater the rainfall the larger the slides, so that when a very large slide is fouud 

 we know that when the slide occurred there was a very large rainfall. Now, as vege- 

 tation begins very soon to cover a land-slide after it has subsided, it follows that the 

 age of a slide occurring in past seasons can be approximated by ascertaining the age 

 of the vegetable growth above it. For instance, if we find that a very large slide has 

 occurred in some place we know that there must have been a very large rainfall the 

 year that the slide moved, and if we find a tree a hundred years old growing on the 

 slide we know that it must have been over a hundred years since the great rainfall 

 came which made the slide. 



A good illustration of this is furnished by the experience of Mr. J. B. Campbell, who 

 found the remains of a very large land-slide on Town Creek, near Pittsburgh, about 10 

 miles from the fishery. The size of this slide indicated that when it occurred there 

 must have been as great a flood as there was last winter. Now, there was a tree grow- 

 ing on this slide which on being felled was fouud to be two hundred years old. We 

 know, therefore, that upwards of two hundred years ago there was a season when there 

 was a vorv heavy rainfall. 



