USGS Earth Science Photographic Archive digital file: hjk00676
Parts of the upper Navajo Sandstone display unusual polygonal jointing and weathering. The pattern may reflect expansion from the unloading of overburden as erosion continues to wear away the landscape. Late Tertiary volcanoes blanketed much of the southeastern Aquarius Plateau, but erosion has stripped away this volcanic cover from large parts of the region. Boulders of basalt occur in stream gravels throughout the central Utah region. Note the lack of cross bedding in this massive sandstone unit compared with the detailed bedding of the photograph below. Exposures of polygonal jointing like this also occur along the Burr Trail, east of Boulder, Utah.
