THE GEOLOGY OF the Olympic Peninsula offers a fascinating glimpse into the massive forces of nature that shaped this land into one of the most complicated rock piles in the world.
It began under the Pacific Ocean, where a collision of tectonic plates scraped together and uplifted massive piles of sedimentary, metamorphic and igneous rocks thousands of feet above the ocean.
As the land rose, it blocked the prevailing winds, causing clouds to gain altitude and release their moisture in the form of rain and snow that flows back to the ocean in a water cycle.
That’s why there’s a rainforest on the west slope of the Olympics and a rain shadow on the east.
The glaciers and rivers are eroding the mountains back down to the ocean. Currently, the Olympics enjoy an equilibrium of uplift and erosion that could change at any time given the vagaries of climate and plate tectonics.
Don’t worry. We’ll be dead long before that happens.
Meanwhile, we’ll have to deal with the geologic cards we were dealt in the last ice age. When parts of Washington state were covered with thousands of feet of ice that flowed from Canada as well as our home-grown glaciers that came down the Olympic river valleys, sometimes clear to salt water.
The Olympic glaciers melted before the massive continental glaciers that filled the Strait of Juan de Fuca and Puget Sound.
The runoff from our glaciers created huge lakes in the foothills in the Olympics.
Other lakes were formed by terminal moraines. These are piles of rocks pushed up by the glacier that were left high and dry when the glacier melted. Lake Quinault is a beautiful example.
There were similar lakes in the Bogachiel and Hoh River valleys, but when these rivers eroded through the moraines, the lakes disappeared, although not without a trace.
In the still waters of the lakes, the glacial till or rock flour that was produced by the glaciers scraping their way down the mountains flowed downstream and settled to the bottom of the lakes, forming thick beds of clay, causing us nothing but trouble to this day.
It’s the reason that driving U.S. Highway 101 south of Forks is like riding a bucking bronco.
Much of the road bed is cracked and sinking because it was built on clay that is slowly but surely sliding back down into the rivers.
This is nowhere more apparent than the current bridge project along the Bogachiel River, where it looks like the crew is working in a big pool of wet concrete.
Just south of the Bogachiel bridge job along the Hoh River, there is a massive mountain of clay creeping across the highway just around a blind corner. Caution is advised.
Meanwhile, the Upper Hoh Road has washed out, again. This, after the Federal Highway Administration just spent three years and an estimated $38 million dumping concrete in the river to protect the road in what was, obviously, all the wrong places.
The Upper Hoh Road is the only access to one of the most popular destinations on the Olympic Peninsula, the Hoh Rainforest.
According to the PDN, 104,176 vehicles passed through the fee station at the Olympic National Park boundary in 2024. The washout is a drastic blow to park funding, regional tourism and the environment.
Originally, there were three types of rocks in the Olympics: igneous, sedimentary and metamorphic.
We’ve added a fourth: asphalt. The asphalt from the road is washing into the spawning beds of the salmon and steelhead as you read this.
I hope someone is studying the problem.
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Pat Neal is a Hoh River fishing and rafting guide and “wilderness gossip columnist” whose column appears here every Wednesday.
He can be reached at 360-683-9867 or by email via patnealproductions@gmail.com.
