242 J. /.. liicJi — Recent Stream Trenching in the 



power to cut where before deposition was in progress. Good 

 sized bowlders will be carried down and strewn along the 

 Stream courses and over the flats. The result of such floods 

 would be manifest in the trenching of the valley hottonis and 

 the spreading out over the flats of bowlders larger than those 

 iu the valley fill itself*. They would produce conditions exactly 

 the same as those we have described as characteristic of the 

 valleys of the Silver City quadrangle. 



Having been led to the belief that a removal of the vegeta- 

 tion cover would be competent to cause stream trenching, it 

 becomes pertinent that we inquire whether there is evidence 

 of such a removal of cover in the region under discussion. 

 The answer is in the affirmative. 



An efficient cause for the removal of such a vegetation 

 cover is the excessive grazing to which the country has bepn 

 subjected during the past few years. A good account of the 

 former conditions of the region was given me by Mr. Mac- 

 Millan, a rancher living in the Mangas valley, who has been a 

 resident of the region since 1876. His statement of the early 

 conditions is substantiated by that of all the old residents of 

 the neighborhood with whom I had occasion to talk. Accord- 

 ing to him there was formerly much more timber than at present 

 along the Mangas valley and on the piedmont desert fans, but 

 probably never enough to modify materially the run-off of the 

 water. More important than the timber, there was, along the 

 valley bottoms, as well as on the hills and desert fans, a thick 

 carpet of grass. This is reported to have been about knee 

 high and quite thick. Along the valley bottoms it was thick 

 enough to be cut for hay by the ranchers. 



Such were the conditions in places where now scarcely a 

 spear of grass can be found. The cattle, often forced to 

 extremes of hunger so great that, sometimes, in a single season, 

 as during the past year, they die by the hundreds of starva- 

 tion alone, have kept the grass eaten so closely that there has 

 been little opportunity for natural maturing and seeding, with 

 the result that not only has the grass been kept closely cropped, 

 but it has been to a large extent exterminated. The vegetation 

 cover has been reduced from one of relatively high efficiency 

 to almost nothing. 



Coincident with the removal of the vegetation has come an 

 increase in the violence of the floods. In the early days, 

 according to MacMillan and others, heavy floods were rare. 

 The storms were just as severe as now, but the run-off was 

 slower. For instance, when a heavy storm occurred in the 

 Burro Mountains, at the head waters of the Mangas, the water 

 would continue to come down the valley for two or three days, 

 whereas now it all comes at once in a single flood. When 



