17 July 1987
Vol 237, Issue 4812

About The Cover

Cross-bedding in the Navajo sandstone in Zion National Park, Utah. These inclined beds formed when sand avalanched down the flank of a large dune. The dip direction of such beds commonly is used to infer paleotransport directions, but experiments demonstrate that bedforms often do not face toward the transport direction. See page 276. [David M. Rubin, U.S. Geological Survey, Menlo Park, CA 94025]