Natural Resources Management and Environmental Sciences Department
BS in Earth Sciences
The Iron Canyon Valley, located at the southern end of the eastern Sierra Nevada at the boundary between the Mojave and Basin and Range tectonic provinces, exhibits clear evidence, over graded timescales, of development through monoclinal shifting, which is the tendency of streams flowing parallel to strike over sedimentary rocks to shift down-dip. Although the character of the valley and bedrock dip indicates development through monoclinal shifting, the current stream network is located up-dip on the east side of the valley. Mapping the surficial geology of the valley revealed the presence of dissected alluvial surfaces approximately 85 meters above modern channel on the east, up-dip side of the valley, and 12-25 meters above the channel on the west, down-dip side of the valley, indicating westward, down-dip channel migration with incision throughout most of the Quaternary. However, undissected terraces and modern channel alluvium record subsequent late-Quaternary drainage shifting to the east side of the valley, where the channel is currently incising into toes of coalesced alluvial fans originating from the east in the El Paso Mountains. Several processes that promote valley asymmetry, including microclimate influences and alluvial fan propagation from the west, are explored to explain the distribution of surficial sediments. It is concluded that late-Quaternary onset of tectonic tilting towards the east has forced the axial channel up-dip and to the east side of the valley. As the area sits astride two major tectonic boundaries, there are a number of processes that could cause tectonic tilting. Further study should consist of: (1) expanding the study to determine if late-Quaternary eastward channel migration is a regional phenomenon, and (2) establishing age control on units Qal1, Qal2, and Qal3 to determine the timing of up dip channel migration relative to nearby fault activity and seismicity.