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• <br />• <br />• <br />Spring 2011 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />The total maximum horizontal strain (maximum extension) over the 280 -foot area during 2007 <br />and 2008 was 16.0 inches, or 1.33 feet. In spring 2009 this value was slightly less at 15.0 inches, <br />or 1.25 feet. Observations during the last four field visits (fall 2009 through spring 2011) have <br />found the total horizontal strain to be consistent with that observed in 2007 and 2008 (i.e., 1.33 <br />feet). Assuming that extension only occurs at crack locations (a valid assumption in these brittle <br />sandstones), the maximum calculated cumulative strain over the area is therefore 1.33 feet <br />divided by 280 feet, which equals 0.00475 (or 0.48 percent). <br />5.12 Photographic Observation Points 4 and 5 <br />These photographic observation points were visited during the spring 2011 as they have been for <br />the past seven years. Photographs were obtained from each of these locations and compared to <br />those from previous visits. No observable changes were noted from those obtained in 2010. For <br />comparisons to earlier years, see discussions for these Photographic Observation Locations in the <br />spring and fall 2009 subsidence reports. <br />5.13 Photographic Observation Point 6 <br />This photographic observation point was not visited during the spring 2011 field visit. <br />Photographs will be obtained from this location during the fall 2011 field visit. <br />5.14 Photographic Observation Point 7 <br />This location was established on September 27, 2007 at the MCC landslide monitoring station <br />that overlooks Monument Dam and Minnesota Reservoir for reference purposes (Map 2). From <br />this location, various features associated with a relatively large landslide south of the Minnesota <br />Reservoir can be readily identified including the head scarp, hummocky topography, and <br />numerous spring and wetland areas indicating discharge locations for water stored within the <br />landslide mass. Figure 32 provides a spring 2009 overview of Minnesota Reservoir, Monument <br />Dam, and the landslide area to the south (distant side) of the reservoir. <br />831 - 032.793 <br />September 2011 <br />Wright Water Engineers, Inc. Page 40 <br />