Abstract
Fabric of rockslide avalanche deposts, the topic of this paper, has been largely overlooked because of other more prominent geomorphological features which mass movements of these type exhibit. For rockslide avalanches such as the Cascade Springs slide originating from the Lower Cretaceous hogback which circumscribes the Black Hills of South Dakota and Wyoming and for the Lower Gros Ventre slide in northwestern Wyoming the attitudes of the long axes (A-axes) of boulders reveal a dominant longitudinal fabric (A-axes parallel to flow). Conversely, boulders at the toe of the Lower Gros Ventre slide exhibit a transverse fabric (A-axes perpendicular to the flow).
In addition, a crude fabric exists for boulders comprising the Lakota orthoquartzite blockfields which mantle the Permo-Triassic Red Valley of the northern Black Hills. It was found that the long axes of the boulders point to the parent material, the Lakota Formation, which crops out on the hogback, up to 4 km (2.5 mi) away. Although most of the geomorphological evidence has been largely destroyed, the crude fabric suggests that the block-fields are relict rockslide avalanche deposits derived from the hogback. Furthermore, fabric may be used as a valuable tool to facilitate identification of other relict mass movement deposits.
