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Geology of the National Parks

GEOLOGY OF OLYMPIC NATIONAL PARK:
PART I OLYMPIC GEOLOGY

Clam and snail fossils
Fig. 21. Fossil shells of clam and snail

Development of a Geologic Map (cont.)

Another important piece of the puzzle was contributed by Richard Stewart, a zealous geology student who mapped the difficult tree-covered terrain of the western core. Stewart showed that these rocks too were complexly disturbed, although less so than rocks in the core to the east. He also carefully analyzed the sedimentary features of the rocks to show that the sandstones and shales were probably deposited by density currents near the continent in a thick wedge of sediment called a submarine fan. Credit for the geologic mapping of the Olympics should go also to the paleontologists who worked with fossils collected by the mappers. In particular, Weldon Rau, a paleontologist for the state of Washington and a field mapper in his own right, studied hundreds of samples of shale to identify Foraminifera shells (fig. 18). The ubiquity of Foraminifera in marine rocks and their rapid evolutionary changes help to distinguish beds of different ages, and the study of these small shells has been a tremendous aid to the geologists in trying to untangle jumbled beds.

One of the young geologists with Charles Park's team of manganese mappers was a perambulatory and persistent New Englander named Wallace Cady. Like Danner, Cady had started in the Olympics as a Boy Scout. His love of the mountains brought him back not only after graduate school to accompany Park in his explorations but again in the 1960s to head a third Geological Survey team that began systematic mapping of the northeastern part of the range. Our work, later expanded to all the enigmatic rocks of the Olympic core, forms the basis of ideas set forth in this book. We were greatly aided not only by all the work that preceded us, but also by new tools: new concepts in sedimentary processes, a new and exciting theory of earth evolution   and the helicopter!

Cutting and stacking cookie dough bed
Fig. 22. Cutting, stacking, and folding cookie dough "bed"

Ideas of Today

Mapping the core rocks has clarified several problems. Except for the ancient rocks at Point of Arches, no rocks older than those of the Eocene basaltic horseshoe and some minor sandstones and shales underlying it have yet been found in the core. A fair number of Foraminifera in red limestone from scattered places in the core appear to be no older than Eocene. One fossil clam shell and several snail shells (fig. 21) from near The Needles have been dated by paleontologist Warren Addicott. They are definitely Eocene and probably late Eocene. The scarcity of fossils in the core rocks is somewhat mysterious, but metamorphism and deformation probably have destroyed the fragile shells. Less metamorphosed rocks to the west contain many more microfossils, and as earlier workers surmised, some are as young as Miocene. We now know that the core is made up of arcuate belts of rock roughly concentric with the basaltic horseshoe and separated from it and from each other by faults. The rocks of these belts are highly folded, broken, and metamorphosed. The most intense disruption and the greatest metamorphic changes are near the center of the bend in the horseshoe. A fault or series of faults bounds the disrupted core rocks on the south in much the same way the Calawah and other faults bound them on the north (figs. 16, and geologic map). In spite of the folding and breaking of the core rocks, most of the original tops of the beds (that is, the direction that was up when the sediments were deposited on the ocean floor) face away from the core of the range. The pattern still looks like a simple anticline, but it cannot be, for the core rocks are not older than the flanks (fig. 17). Charles Park appears to have been correct when he suggested that the thick mass of core rocks was thickened by fault slicing The whole pile can be likened to a sheet of cookie dough, cut up into pieces (by faults), then piled up in a stack (by thrusting), turned on edge, and bent (fig. 22). To find a plausible explanation for this extreme rock deformation and Olympic structure in general, we must digress from Olympic rocks and examine some of the newer ideas about earth evolution.



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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