Surficial geology, geomorphology, and erosion of archeologic sites along the Colorado River, eastern Grand Canyon, Grand Canyon National Park, Arizona

Application of sedimentary-structure interpretation to geoarchaeological investigations in the Colorado River Corridor, Grand Canyon, Arizona, USA

“…Many cultural sites located in or on sediment deposits are actively eroding because of aeolian deflation and incision by gullies (Leap et al, 2000;Neal et al, 2000;Fairley, 2003). Hereford et al (1993) suggested that gully incision of sediment deposits, and the base level to which small drainage systems respond, were linked to dam operations; they hypothesized that pronounced arroyo incision was caused by lowering of the effective base level at the mouths of ephemeral drainages to meet the new, post-dam elevation of high-flow sediment deposition, ∼3-4 m below the lowest pre-dam alluvial terraces. Thompson and Potochnik (2000) modified this hypothesis to include restorative effects of fluvial deposition in the mouths of gullies and arroyos, which raises effective base level, and new aeolian deposition on pre-dam alluvial deposits as wind reworks flood-deposited sand.…”

Gullying and erosion control at archaeological sites in Grand Canyon, Arizona

“…Hereford et al (1993) recognized that a period of more intense precipitation from the late 1970s through the 1990s may have driven the accelerated erosion. But these studies also raised the idea that increased erosion is linked to Glen Canyon Dam, which altered base level for some gullies and started controlling the hydrograph of the Colorado River in 1963.…”

“…Although erosion is an expected part of larger cycles of aggradation and degradation in the southwestern USA, studies have shown that gully incision in Grand Canyon increased between 1973 and 1984 (Hereford et al, 1993;Thompson and Potochnik, 2000). Hereford et al (1993) recognized that a period of more intense precipitation from the late 1970s through the 1990s may have driven the accelerated erosion.…”

“…Hereford et al (1993Hereford et al ( , 1996 studied the Holocene alluvial stratigraphy of the river corridor and found that most cultural sites are located in middle-late Holocene deposits they called the 'alluvium of Pueblo II age' and the 'striped alluvium' (Figure 1). These deposits generally have not been inundated by historic unregulated (pre-dam) flows of the Colorado River, but have been modified by aeolian processes.…”

Ecosystem Modeling for Evaluation of Adaptive Management Policies in the Grand Canyon

“…Perhaps the most important issue here is the erosion of archeological sites by arroyo cutting in short, ephemeral streams that drain the terraces of the river corridor (Hereford et al 1993). The reduction of sediment load and elimination of the annual flood in the post-dam era may have reduced the elevation of depositional environments and are hypothesized to intensify arroyo cutting and accelerate the exposure of archeological sites.…”