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Geology of the National Parks


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Obstruction Peak Road

STOP 13: Deformed rocks

The view across the valley of Grand and Moose Lakes from the trail gives the hiker the impression of very disordered geologic structure (fig. FT 26). Cliffs and pinnacles of resistant sandstone beds stand out patchily on the ridge southeast of the valley. In a normal succession of sandstone and shale, even if uptilted or folded, the pattern of the bedding revealed by erosion would probably be discernible in a view like this. Here, however, the continuity of strata has been disrupted. The rocks are folded, and the beds and folds have also been pulled apart along many small faults. Isolated masses of resistant sandstone beds remain in the broken slate.

Deformed rocks above Grand Valley
Fig. FT 26. View across Moose Lake, Grand Valley, showing masses of resistant sandstone in a mush of slate.

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Material in this site has been adapted from Guide to the Geology of Olympic National Park by Rowland W. Tabor, of the USGS. It is published by The Northwest Interpretive Association, Seattle.

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