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Shinarump Conglomerate
The early Late Triassic conglomerate called the Shinarump Conglomerate, formally the ''Shinarump Member of the Chinle Formation'', is a highly resistant coarse-grained sandstone and pebble conglomerate,〔Blakey, and Ranney, 2008. ''Ancient Landscapes of the Colorado Plateau'', subsection, ''Great River Systems of the Moenkopi and Chinle: Triassic Deposition,'' pp. 58-66, p. 64〕 sometimes forming a caprock because of its hardness, cementation, and erosion resistance. The Shinarump is found throughout the Colorado Plateau with significant exposures as the canyon rimrock in the vicinity of Canyon De Chelly National Monument, at the north-northeast of the Defiance Plateau/Defiance Uplift. At Canyon De Chelly the Shinarump Conglomerate was laid down upon De Chelly Sandstone-(280 Ma, an erosion unconformity of 50 my), in a region at the west foothill region of the mostly north-south trending Chuska Mountains of northeast Arizona – northwest New Mexico.
Just northwest of Canyon De Chelly, the Shinarump also forms a caprock in Monument Valley across the border region of northern Arizona – and southern Utah. The Shinarump Conglomerate there is laid upon units of the Moenkopi Formation and remain as resistant caprocks preserving the vertical cliffs of De Chelly Sandstone and other units of the Monument Upwarp/Monument Uplift. The associated Black Mesa (Arizona)-Defiance Uplift extends southeast from Monument Valley into the western border region of New Mexico. The relatively steep east dip of geology units results in increasingly younger geologic units eastwards into New Mexico.
==Monument Valley and Canyon De Chelly caprock==
In Monument Valley, of Arizona and south Utah, only larger landforms still contain the protective caprock of the Shinarump Conglomerate. The vertical cliffs of highly resistant De Chelly Sandstone protect the highly erodable Organ Rock Formation that forms 'erosion skirts' at the base of the vertical monuments in Monument Valley. For larger mesas, or larger connected land forms, where the more erodable overlying Moenkopi Formation, has not been lost, (with the caprock Shinarump also being undermined), larger sections of Shinarump are thus preserved. Perimeter mesas in the Monument Valley region have the caprock protecting the upper surface, plants, and alluvium from easy erosion of the landform surface.
At Canyon de Chelly, the trail to White House Ruin,〔Lucchitta, 2001. ''Hiking Arizona's Geology'', Hike 10, ''White House Ruin Trail'', pp. 111-113.〕 descends through the Shinarump Conglomerate, but also has a tributary slot canyon landform with large accumulations of the Shinarump erosional debris on the slot-canyon floor. The trail then descends through the cross–bedded cliffs (fossil sand dunes) of the De Chelly Sandstone.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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