USING SURFICIAL GEOMORPHOLOGY, SOIL DEVELOPMENT, AND STRATIGRAPHY TO ESTIMATE THE TIMING AND MEANS OF INCISION OF AFTON CANYON, MOJAVE DESERT, CA

Preliminary Quaternary mapping and soil investigations appear to suggest a more complicated evolution of Afton Canyon than previously proposed. Inset within the lower half of Afton Canyon, below the base of the Manix Formation, are three lacustrine deposits. Although the lacustrine interpretation may be equivocal for two of the deposits, in all three locations these deposits overlie fluvial terraces indicating a cycle of cutting, filling or temporarily damming, and then continued incision as a mechanism of canyon cutting. In this narrow, fault controlled canyon, three possible causes are: 1) storm driven landslides; 2) tectonically driven landslides; or, 3) motion along the Manix Fault. In addition, mudflow deposits inset within the canyon transport large boulder to cobble sized pieces of lake sediments, alluvium with intact stratigraphy, and Tertiary fanglomerate. Do these deposits relate to breaking temporary dams, or are they common deposits in this type of landscape?

Soil development into a north rim fluvial terrace deposit suggests a relatively older age than those fluvial terraces inset within the canyon, and perhaps infers overflow occurred before the inset strath terraces were formed. Based on previous investigations, these lower strath terraces are thought to have been deposited shortly after the late Pleistocene highstand of Lake Manix 21-18 ka (Meek, 1999). This leads to the questions: Is this soil truly reflecting an age difference or variations in soil development? Could there have been fluvial deposition without the Mojave River exiting the Lake Manix Basin? If this fluvial terrace could only be deposited with the contribution of the Mojave River and the soil developed into this terrace does reflect an older age, then there may be three times when Lake Manix and at least the downstream Soda Lake basin had a hydrologic connection. This includes a much older overflow proposed by Reheis and Redwine (2005) and the previously known overflow involving the draining of Lake Manix studied by many (e.g. Buwalda, 1914; Ellsworth, 1932; Meek, 1990; Enzel et al, 2003).

Detailed stratigraphic and soils geomorphology investigations were initiated to study the timing and evolution of Afton Canyon. Work to date delineates a complex geomorphic history and has led to more questions than answers, but fieldwork is ongoing.