80 C. E. KEYES INTERMONT PLAINS 01" THE ABID REGION 



increasing in volume ; tlie teamster was startled, and set out along the road 

 up the yalley at best speed, but before he had gone 100 yards the flood was 

 about him. The water was thick with mu&, slimy with foam, and loaded with 

 twigs, dead leaflets, and other flotsam ; it was seen up and down the road 

 several hundred yards in either direction, or fully half a mile in all, covering 

 the entire surface on both sides of the road, save a few islands protected by 

 exceptionally large mesquite clumps at their upper ends. The torrent ad- 

 vanced at race-horse speed at first, but, slowing rapidly, died out in irregular 

 lobes not more than a quarter of a mile below the road; yet, though so broad 

 and tumultuous, it was nowhere more than about 18 inches, and generally only 

 8 to 12 inches, in depth, the diminution in depth in the direction of flow being 

 less rapid than the diminution in velocity. The front of the flood was com- | 

 monly a low lobate wall of water, 6 to 12 inches high, sloping backward where | 

 the flow was obstructed by shrubbery, but in the open curling over and break- I 

 ing in a belt of foam like the surf on a beach; and it was evident that most ', 

 of the water first touching the earth as the wave advanced was immediately 

 absorbed and as quickly replaced by the oncoming torrent rushing over pre- I 

 viously wetted ground. Within the flood, transverse waves arose constantly, |, 

 forming breakers with such frequency as to churn the mud-laden torrent into I 

 mud-tinted foam ; and even when breakers were not formed it was evident | 

 that the viscid mass rolled rather than slid down the diminishing slope, with | 

 diminishing vigor despite the constant renewal from the rear. Such were the i 

 conspicuous features of the sheetflood — a thick film of muddy slime rolling | 

 viscously over a gently sloping plain ; and this film was a transformed stream I 

 still roaring through the rugged barranca only a few miles away." i 



i 



The verity of tlie tremendo"us efficiency of the floodsheet has been amply \ 

 attested by the experiences, for the past 20 years, of the railways travers- | 

 ing the Mexican tableland and the Great basin of western United States. | 

 Sheetflood effects have not attracted special attention mainly for the 1 

 reason that when interfering with railway travel they are spoken of i 

 merely as "washouts." Of late years the various roads of the arid region ' 

 of the West have expended very large amonnts of money devising means '< 

 of protection against the "floods." This is sought by attempting to 

 direct the waters into artificial streamways. On the more elevated sides 

 of the tracks are constructed long series of deep A-shaped ditches and 

 high embankments. Where the bases of the contiguous triangles meet, ' 

 trestles are built. 



The railways, in other words, are making every endeavor to develop on 

 the plains stream systems such as nature produces in the humid lands. [ 

 Success is only partial. The plain-forming forces are stronger than 

 man's weak efforts against them. The ever-shifting sands and loams are j' 

 continually filling up the ditches and leveling off the embankments, i 

 When the sheetflood comes it rolls over the plains and buries the tracks I 

 or floats them off. It works in the same way as it has for centuries. ! 



