Laserfiche WebLink
Spring 2009 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />• units due to longwall mining can cause reduced formation stability and thus lead to cracking and <br />slabbing of the brittle sandstone unit, particularly at the outcrop where there is no lateral support. <br />As a result, Location 5 is an expected corollary to the rockfall /landslide area on the west side of <br />West Flatiron new Location 4. While noticed for the first time during this fall 2008 field visit, it <br />is likely that the cracking and slabbing of the sandstone outcrop on the east side of West Flatiron <br />has been occurring for at least a year. <br />is <br />Figure 19. Fall 2008 view of a sandstone outcrop on east side of West Flatiron showing fractures <br />and rockfall where cracks, previously noted at Location 4, intercept the rock face. The historically <br />observed crack trend from Location 4 is generally from the while pickup truck (background) toward <br />the rockfall (foreground). The sandstone cliff at this location is 40 -50 feet thick. <br />Figure 20 is a view of approximately the same location taken in Spring 2009 showing relatively <br />little change since our first observation of the area in October 2008. <br />831- 032.791 W right Water Engineers, Inc. Page 33 <br />November 2009 <br />