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<br />. <br /> <br />. <br /> <br />John W. Re1d <br />Page 2. <br />July 23, 1973 <br /> <br />been placed much earlier. The original failure involved a width of about 150 <br />feet and a downslope extent of approximately 100 feet. The mass that slid at <br />this location was approximately five feet in thickness, and therefore the volume <br />of the original slide mass is estimated at roughly 2,800 cubic yards. Mud from <br />this original failure slid downward across the old Daniels Hill Road. The old <br />road was for the most part cut into shale bedrock and had a relatively small <br />amount of fill at its outer edge, consequently the old road bed remained intact <br />except for some erosion of the outer fill embankment. Below the old road, part <br />of the land traversed by the slide mass was eroded and part was covered with a <br />sheet of mud. The west portion of the area crossed by the sliding mud was cov- <br />ered by a sheet of mud three to four feet in thickness. Immediately to the east <br />of this, friction coupling of the sliding mud tore loose a considerable amount <br />of very wet colluvium that was similar to the original mass. At this point, the <br />mud entered a gentle swale, turned and became.a channeled mudf10w and proceeded <br />downhill continuing to erode and deposit along the route. Part of the mud cross- <br />ed the county road and flowed into Beaver Lake. The additional mud torn loose <br />below the original failure appears to have amounted to 1,000 cubic yards or more. <br />Of the total mud torn loose, 3/4 or more was probably deposited at various loca- <br />tions along the hill slope and swa1e and the rest crossed the county road and <br />entered the lake. <br /> <br />The slide took place quite rapidly. Two persons who were outside in the old <br />townsite reported that they heard a grinding and rumbling sound and that it was <br />allover except for the slow flowage of mud in the lowest area within a few min- <br />utes. Additional indications that the slide was sudden and forceful can be seen <br />in the berm of mud and debris that was thrown up to a height of approximately <br />eight feet on the outside of the first turn that the slide mass made below the <br />old Daniels Hill Road. <br /> <br />Contributing Factors <br />The slide occurred on a very steep slope (ranging from 45% to 75% within the <br />slide area). Bedrock of the area is Mancos shale which is moderately stable, <br />but much of the general area is covered with shale-derived colluvium which may <br />be as thick as 20 feet. The colluvium (a lump term for unconsolidated slope <br />wash, talus, and landslide or creep deposits) is extremely ~stab1e when loaded, <br />oversteepened, or saturated with water. All three of these adverse conditions <br />were present at the site of the slide. A roadfil1 had been placed on the col- <br />luvium at the upper limit of the failure, and'inspection of the site immediately <br />after the incident showed that sheet wash from runoff intercepted by the higher <br />switchbacks had been entering the site from above. Several small streams of <br />water were issuing from the slide scarp when I arrived. The material was so <br />saturated that after the origiona1 slide it continued to move down the swa1e as <br />a mudflow. I am uncertain as to when this exact stretch of road was constructed, <br />but roads in that general area were under construction in late JUde and July of <br />1971 when I was doing field work for our original report on Marble. This was <br />considerably before any detailed geologic studies had been made by consultants <br />for the developers. You will recall in my informal report to you in July of <br />1971 I informed you that the road fill was not being properly placed. There was <br />compaction equipment ,on the site but it was not being used. There was no watering <br />