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Geology of the National Parks

GEOLOGY OF OLYMPIC NATIONAL PARK:
PART I OLYMPIC GEOLOGY

Complex structure in Olympic core rocs on Mt. Fitzhenry
Fig. 19. Complexly disrupted sandstone and shale beds of Olympic Core on north ridge of Mount Fitzhenry.

Development of a Geologic Map

"The great tragedy of Science — the slaying of a beautiful hypothesis by an ugly fact."

 ~ T. H. Huxley, Presidential Address,
British Association for the Advancement of Science 1870

By the 1940s geologists from the United States Geological Survey and geology students from the University of Washington were beginning to fill in more of the geologic map of the Olympics. From 1938 to 1941 an ambitious mapping project was undertaken by a Geological Survey team led by Charles Park, Jr. The government sent him into the Olympics to assess the supplies of manganese, a metal then difficult for the United States to obtain because of world conflict. As they searched for manganese minerals, Park and his team of young geologists also ferreted out almost all the outcrops of basalt and greatly improved the geologic map of most of the basaltic horseshoe, outlined earlier by Weaver.

Highly disrupted sandstone beds
Fig. 19a. Highly disrupted sandstone and shale beds, now blocks of semischist in a matix of phyllite, Olympic Core.

Although Park was interested primarily in the manganese and its origin, he recognized that the simple anticline theory was not quite right. First, clam shells of probable Oligocene age had been found near Mount Appleton, well within the mountainous core. This further confirmed that at least some rocks in the core were younger than the basalt flanks of the so-called anticline. Second, Park recognized the complexity of faulting in the core rocks (fig. 19, 19a) and suspected similar complexities in the basaltic horseshoe, especially on its east side. He thought that the core sandstone and slates, as well as the basalts, appeared much thicker than they originally were because they had been cut and doubled up by faulting (fig. 21).

Not long after Park's work, an intense student from the University of Washington, Wilbert Danner, began mapping in the Olympics. Danner had fallen in love with the Olympics as a Boy Scout. In 1955 he summarized Olympic geology in a booklet (Geology of Olympic National Park, 1955--long out of print) that became the definitive work on Olympic geology for geologists and nongeologists alike. Danner still believed the mountains were an anticlinal feature, with older rocks in the core; but he reported the possibility that younger rocks were there too.

Needles of the Inner Basalt Ring
Fig. 20 Basalt of the Inner Basalt Ring in the Needles, shown on the right.

By the 1950s more students from the University of Washington were thrashing through the underbrush on the east and south sides of the mountains, and a more coherent picture of Olympic geology was evolving. By that time it was clear that the inner Olympics are partly ringed by Eocene basalt, the Crescent Formation, forming an aggregate of ridges called the basaltic horseshoe. The rocks outside the basaltic horseshoe and overlying it are mostly sandstone, shale, and conglomerate. Although folded and faulted, they are nowhere as disturbed as the rocks within the horseshoe. Within the core is a second partial, broken ring of basalt, called the Inner Basalt Ring (figs. 16, 20).

Meanwhile, another Geological Survey team consisting of Robert Brown, Jr., Howard Gower, and Parke Snavely, Jr., was wading up and down the creeks, crawling through the brush, and scrambling over the northern foothills of the Olympics. Since the early days of Albert Reagan, many new roads had been cut through the thick Olympic forest, greatly improving the geologists' chance of reaching outcrops. The team was able to gather many new data, plot them on modern topographic maps, fit them together with earlier pieces of information, and finally produce a coherent history of the rocks along the northern periphery of the mountains. One significant discovery of the U S Geological Survey mappers was the Calawah fault zone (fig. 16). This zone of highly broken rocks and some smaller faults separate the relatively simple rock structures of the north periphery from the more complex ones of the core. Recognition of the fault zone suggested the possibility that the rocks reportedly younger than the Eocene basalt were brought into the core by fault movement.


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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