PROBLEMS FROM LAND OCCUPANCY 183 



and in parts of the drainage basins the slopes approach 100 

 per cent. The mud-rock flows are water-lubricated, viscous 

 masses of rock fragments that flow slowly down these can- 

 yons. Observations of small flows in recent years indicate 

 that they are generated in bare areas that may be only a frac- 

 tion of 1 per cent of the drainage basin. 



Man has been credited with entire responsibility for cre- 

 ating conditions favorable for this destructive erosion, by 

 removing the protective cover. Evidently the floods of 1923 

 and 1930 in Ricks Creek and Parrish Creek spewed ma- 

 terials directly onto glacial lake sediments and were thus 

 the first such occurrences since the waning stages of the 

 glacial Lake Bonneville, thousands of years ago. Recent 

 geologic studies have shown, however, that geologic, topo- 

 graphic, and climatic conditions were favorable for such 

 flows long before man appeared on the scene. Before settle- 

 ment, mud-rock flows occurred in Centerville Canyon, 

 which has not produced a mud-rock flow in the past century. 

 Wells in the valley area penetrate hundreds of feet of mud- 

 rock sediments, and the Wasatch Range has remnants of a 

 deep, well-developed soil which was largely removed before 

 Lake Bonneville reached its maximum level. Since the re- 

 cession of that lake, the mountains have been raised as 

 much as 75 feet with respect to the valley, along a fault that 

 follows the base of the range throughout Davis County. 

 The resulting increase in gradient has undoubtedly con- 

 tributed to the severity of erosion and deposition in the 

 1923 and 1930 floods. 



The first work in the experimental area was on the 

 "sore" spots that could start mud-rock flows. Contour 

 trenches were dug; check dams were constructed in in- 

 cipient gullies; many other devices were placed to hold 

 back overland flow. In subsequent years, programs of re- 

 seeding and reforestation have refined the control over 

 surface runoff. The accomplishments have been great, and 

 the valley residents have far greater assurance that their 

 real-estate investments will not be wiped out. The steep 



