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Unveiling Washington State's Roadside Geology: A Rockin' Adventure Across Time

Buckle up, fellow hikers and geological enthusiasts for a riveting journey through the geological wonders that flank the I-90 highway in our state. Washington's I-90 is not just a road; it's a geological time machine that takes you on a thrilling ride through eons of Earth's history. Get ready to uncover the secrets of ancient volcanoes, colossal ice sheets, and the dramatic forces that shaped this breathtaking landscape. Let's hit the road and explore the fascinating roadside geology of Washington!

photo credit: Steven Pavlov

The Cascadia Subduction Zone: A Volcanic Adventure

Our geological escapade begins with an explosive bang – quite literally. On the western side of the state the mighty Cascade Range comes into view. These towering peaks, like sentinels guarding the land, are part of the Cascadia Subduction Zone. The Cascadia Subduction Zone unfolds as a captivating geological narrative, weaving a tale of tectonic intrigue along the Pacific Northwest. Beneath the serene landscapes lie subterranean forces, where the Juan de Fuca Plate plunges beneath the North American Plate, triggering seismic drama and volcanic prowess. This volatile embrace has birthed towering volcanoes like Mount St. Helens, Rainier, and Hood, each with a fiery history etched into their slopes. These peaks, once mighty giants, remind us of the relentless dance between Earth's crustal plates. The geological stage of Cascadia is a testament to both its dynamic past and the potential for future upheavals, shaping a truly volcanic adventure.

The Dance of the Ice Ages

Fasten your seatbelts for a plunge into the icy embrace of Washington's glacial history. I-90 traverses regions once buried under colossal ice sheets during the Pleistocene epoch. Carved by colossal glaciers over 10,000 years ago, the landscape boasts striking features like U-shaped valleys, deep fjords, and towering mountains. The stunning beauty of Snoqualmie Pass, for instance, is a testament to the dynamic dance between ice and rock that shaped this striking landscape. The iconic Mount Rainier, a dormant stratovolcano, is crowned with glaciers that shaped its contours during the Ice Age. These geological wonders stand as timeless markers of Earth's transformation, illustrating the immense power of ice and water in shaping the terrain, while allowing us to connect with the ancient forces that once ruled the land.

Basalt Columns and Ancient Lava Flows: Nature's Artistry

You will notice the intricate hexagonal patterns adorning the cliffs along the highway. Millions of years ago, molten lava surged across the landscape, cooling and contracting to form remarkable hexagonal basalt columns. These towering rock formations, resembling a grand organ or towering cathedral pipes, stand as a testament to the earth's creative forces. These ancient lava flows, frozen in time, offer a glimpse into the Earth's fiery past while captivating the imagination with their precision and grandeur. A scenic reminder of our planet's artistic history etched in stone. From the imposing Cle Elum Pinnacles to the mesmerizing Teanaway Columnar Basalt, the rocks themselves narrate tales of ancient volcanic eruptions and tectonic forces.

Fossils and Prehistoric Marvels: A Glimpse into Earth's Past

In the heart of the Cascade Mountains, the Thorp Gypsum Quarry reveals a treasure trove of Eocene-era fossils, including 50-million-year-old horse skeletons and unique plant imprints. Discover the John Day Fossil Beds National Monument, a time capsule of the Cenozoic era, showcasing mammal fossils like the mighty three-toed horse and the ancient rhino-like Uintatherium. The Gingko Petrified Forest State Park is a treasure trove of petrified wood, with logs transformed into stunning agate and jasper. Nearby, the Teanaway Community Forest holds the secrets of the past with fossilized leaves and prehistoric insects.

Ancient Basalt Flows and the Columbia River Gorge

As you near the Columbia River, the landscape transforms yet again. Gaze upon the dramatic basalt cliffs that encase the river, telling tales of colossal lava flows that erupted thousands of years ago. The towering walls of the Columbia River Gorge showcase nature's sculptural prowess, shaped by both fire and water.

The Legacy of Ice Age Floods

As we journey eastward approaching the Spokane area, the road winds through a landscape shaped by cataclysmic floods. Millennia ago, colossal ice dams, formed by retreating glaciers, periodically gave way, releasing unimaginable volumes of water. These cataclysmic floods surged across the land, carving deep canyons, sculpting valleys, and depositing massive boulders known as glacial erratics. The ripple marks, giant gravel bars, and potholes they left behind are like scars on the land, telling the story of their power. The result is an awe-inspiring topography, including the dramatic chasms of Dry Falls and Palouse Falls. Dry Falls were once ten times the width of Niagara Falls!

Recommended Books for Your Geological Expedition

If this journey through the I-90 roadside geology of Washington State has piqued your curiosity (and we hope it has!), there are some fantastic books that can take you even deeper into the world of rocks, minerals, and the Earth's ever-changing story:

Roadside Geology of Washington by David D. Alt and Donald W. Hyndman

A must-have guide for anyone exploring Washington's geology, this book offers insightful explanations of the state's most captivating geological sites.

Geology Underfoot in Western Washington by David Tucker and Kate Troll

Take a closer look at the geologic wonders beneath your feet with this engaging guide that takes you on a journey through the region's geological history.

Volcano: A Visual Guide by Donna O'Meara

Delve into the explosive world of volcanoes with stunning visuals and in-depth explanations that will leave you awe-inspired.

From the fiery birth of volcanoes to the icy embrace of ancient glaciers, from the whispering secrets of ancient seas to the rumbling echoes of seismic forces, the highway offers a front-row seat to the grand narrative of our planet's evolution. Whether you're a seasoned geology enthusiast or simply a curious traveler, the I-90 geologic adventure promises to be an experience that enriches your understanding of the world around us.

The next time you find yourself cruising along I-90, remember that the landscape outside your window is more than just a picturesque view—it's a captivating geological story waiting to be unraveled. Embrace the curiosity of a geologist, and with each mile, you'll be delving deeper into the pages of Earth's history.

Happy trails while learning Washington's geology!

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