## 3 Results
### Study Site B 3m  
Study Site B (Figure 12) is located along the Glenn Highway near milepost 87 and consists of an ~11 m high road cut, inclined at approximately 50 degrees. The exposed rock slope is approximately 110 m in length. The site includes soft argillaceous rocks (carbonaceous siltstones) of the Chickaloon formation that have been intruded by hard, well-indurated mafic sills (basalt) [56]. A major anti-dip (_i.e._, dipping into slope, with favorable structural control) discontinuity set is defined by the orientation of the contact with the intrusive basalt unit. This dominant set, along with other irregular joint sets in the sill material, produce rock fragments having maximum dimensions in the range of ~20 to ~200 cm. The significant contrast in strength between the siltstone and sill (basalt) materials has resulted in differential erosion features including cantilevered overhanging rocks. No seepage was observed during the fieldwork. Mass wasting along the lower portion of the slope occurs through erosion and raveling of the soft siltstone unit. Within the upper portion of the slope, mass wasting occurs both through release of rocks defined by discontinuities in the sill materials, as well as through tensile fracture and collapse of portions of the cantilevered sill rock. Figure 13a shows a sample triangulated surface model with all holes filled (window size = 50 cells, or 2.5 m) for Site B. The model was generated with a 0.05 m cell size and effectively captures various overhanging features as well as abrupt transitions across the slope. Analysis indicated that 11% (2014) to 15% (2013 data) of rock slope surface area was comprised of holes. Figure 14 shows the rockfall clustering results with different window sizes for hole filling ranging from no holes filled to a window size of 50 cells (2.5 m). Figure 11: (**a**) Comparison of calculated erosion volumes for various resolutions and with (HF) and without (NHF) hole filling for Site A between 2013 and 2014; (**b**) Comparison of rockfall volumes for Site A with varying hole filling search window size. Computations are based on a cell size of 0.05 m. The plateau indicates that the majority of the holes for Site A were small and filled with a window size of 15 cells (0.775 m). Figure 12: Photograph of overhanging rock at Site B. The crest-to-toe vertical height of the slope is approximately 11 m.  
Figure 13: _Cont._  
Figure 14: Evaluation of the influence of varying the hole filling window size (ws) on the resulting rockfall clusters (2013–2014). Note that the figure uses the same coloring scheme as described in Figure 9 with grey representing areas of no significant erosion and white indicating holes in the dataset. For reference, this section is 110 m long. (**A**) no holes filled; (**B**) holes filled (\(\text{ws}=5\)); (**C**) holes filled (\(\text{ws}=10\)); (**D**) holes filled (\(\text{ws}=20\)); (**E**) holes filled (\(\text{ws}=50\));  
Figure 13: Sample results of surface modeling (0.05 m resolution) from the 2014 survey of the exposed rock at Site B with holes filled for the (**a**) west and (**b**) east portions of the site; (**c**) Close-up wireframe model of a section for detail. Figure 15 shows the cumulative magnitude-frequency relationships derived from the clustering analysis of both filled and unfilled models. The form of the magnitude-frequency relationships are  
Figure 16: (**a**) Comparison of calculated erosion volumes for various resolutions and with (HF) and without (NHF) hole filling for Site B between 2013 and 2014. Note that the hole filling window size was adjusted for each cell size analyzed such that it filled smaller holes, but did not fill excessively large holes; (**b**) Comparison of rockfall volumes for Site A with varying hole filling search window size. For this analysis, a constant cell size of 0.05 m was used. Note that at a window size of 50 (2.5 m), all holes are filled so the volume does not vary significantly below that.