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Geology of the National Parks

GEOLOGY OF OLYMPIC NATIONAL PARK: PART Il NOTES ON THE GEOLOGY

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Deer Park - Blue Mountain

STOP 5: Deer Park Road

The banks of the Deer Park Road clearly reveal the layers, or beds, of stratified rock. Etched in relief, they form a decorative wall along the road almost all the way to Deer Park. In many places a regular alternation of light-gray sandstone with dark-gray to black shale is conspicuous; the sandstone beds are hard and angular on the edges and project farther than the softer, darker, somewhat crumbly shale beds (fig. FT 11). These are rocks formed from sand and mud deposited in the ocean about 40 to 60 million years ago.

Thin bedded sandstone on Blue Mountain
Fig. FT 11. Aternating beds of sandstone and shale (rythmite) on Blue Mountain.

On broken surfaces of the sandstone, the sand grains can easily be seen. The much finer grains of the black shale are less easily recognized but the dust produced from a scratched piece of shale is nothing more than dried mud.

At 5.9 miles from the park boundary, where the road begins to break out into the open,thicker beds of sandstone appear. In fact, the road becomes quite rough here and just a little steeper, reflecting the greater difficulty of making a roadcut through these hard beds. High on the mountainside they form conspicuous ribs. A close look at the rocks reveals small, rounded pebbles in the conglomeratic sandstone, remnants of ancient gravels.


On to Stop 6. Blue Mountain

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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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