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Fall 2007 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />• <br />Y1 ~ yy~. <br />. • ~~ r . ~,~.- <br />~ .~,: <br />' o{ `,rte a .#~, ~~'1~, r,., <br />~• ~, <br />c~ L <br />1R. i.9.~~t ~~~1, +'Pl..t <br /> <br />~'. ~ ` <br />.~;r <br />' ~.~'` '. <br />~r,i ~ - i <br />.~~~ ``- <br />``r ' t s <br />~ . • ~~: <br />.C '' ~ <br />. ~ t• ; ~ ~ ~.; , <br />F~ciure 20. Northeastward view of the active rockfall/landslide area above the mined part of longwall panel 21 (fresh <br />looking scarp in right middle ground) and the steep point above mined longwall panel 20 (left middle ground). <br />Photographic observation point 1 is located about midway between the active rockfall/landslide scarp and the steep <br />point to the middle left. <br />5.5.2 Location 8 (Location 9 of the Spring 2007 Field Visit) <br />• <br />*-A P <br />~~ r.~ <br />1• ~ ? , r.. <br />Location ~ (an annual observation location) provides a good, close view of the headscarp of the <br />first eaacrn drainage of Sylvester Gulch that terminate on West Flatiron. 'I-he vie~'<• from this <br />location is of the upper part of the Ohio Creek Member of the Mesaverde Formation (Figure 2 l ). <br />The location, which is in an area with a eery high rockfall potential (see Map 3), is located in the <br />approximate midpoint of mined longwall panel 22 and is 2,200 feet above the elevation of the B- <br />seam. The maximum estimated depth of the cracks on the headscarp is 30 to 60 feet, which is <br />the approximate thickness of the sandstone cliffs. <br />831-032.780 Wright Water Engineers, Inc. Page 34 <br />November 2007 <br />