The Story of Silver Falls State Park--Part 1

This will be a a 7-part series on the geological and historical history of Silver Falls State Park, Oregon's largest state park. The animal and plant life of the park is lacking a bit due to the fact that I got a degree in Geology. What you read below is actually a book I have been working on for a while. I want to include more about the animal and plant life before I publish it. If you wonder how I know so much about the park, it is because I have done extensive research on it. Feel free to give comments or suggestions to make the book better; this preview does not include all the pictures that will be in the book. Also, I am not quite sure why such large gaps occur between paragraphs on this series.

INTRODUCTION

Silver Falls State Park has a 40 million year old history that includes rocky headlands, storm-battered shores, coastal sand dunes, and the rainforest of today. It has witnessed rivers of lava that destroyed the land, the aftermath of a massive volcanic eruption, and the creation of the many waterfalls within the park, five which fall over 100 feet. In Winter, cracks in the surrounding basalt create springs with their own little waterfalls; while in Spring, the Lower South and Middle North Falls create walls of ice cold water that are surrounded by nearby flowers. During Summer, locals come to swim in the pools found at this park; and in Autumn, the brilliant colors of the trees go perfectly next to the silvery-white waterfalls.

THE BEGINNING

The geologic history is said to be read like a book. Each different layer of rock is like a different page in a book, all combining to tell a story of how a place on the Earth was created.

We start the story of Silver Falls State Park 40 million years ago. At that point in time, what would become known as Silver Falls State Park was part of the Oregon Coast. The landscape may have looked similar to that of the Hawaii Volcanoes National Park today. The climate was much warmer and trees that were further inland would have included oak, maple, ginkgo, and possibly metasequoia. Grasses were scarce and the oceans were much warmer than today. The dinosaurs had been extinct for 25 million years already and the mammals were on the rise. A shallow sea existed where the Willamette Valley is today, and the adjacent Coast Range did not exist yet.

The volcanic slopes that are buried deep under Silver Falls State were from the beginning of the Ancestral Cascades. The Ancestral Cascades began forming around the same time as Silver Falls State Park. Their formation was due to the subduction of the Farallon Plate, which would later become the Juan de Fuca Plate, underneath the Pacific Northwest. Now known as the Western Cascades, these early volcanoes formed a line parallel to the Modern Cascades roughly 20 miles to the west. In the early days, these volcanoes were not explosive, steep-sided composite cones like Mt. St. Helens. Instead, they were forming broad mountains called shield volcanoes like Newberry Crater in Central Oregon.

Basaltic lava that flowed down from the western flanks of these early volcanoes eventually reached the sea and created a rock that was harder to erode than the surrounding beaches. During this time, the coastline would have looked more like the Hawaiian coastline as the lava poured into the sea and rapidly cooled after hitting the cool water. One section of the Ancestral Cascade Range, possibly located in the Opal Creek Wilderness, created the Little Butte Volcanics. These were created at the beginning of our story and, without them, our story wouldn’t have started for another 8 million years. The Little Butte Volcanics is buried roughly 2,000’ below where the South Falls Lodge stands today. You can see what they look like if you take a short drive along the North Santiam River to Detroit Lake. These ancient rocks are discolored brown from time and erosion.
 
By 32 million years ago, the basalt coastline of the Little Butte Volcanics would have eroded down to many headlands and sea stacks that stuck up out of the sea. The scenery elsewhere in the state has already dramatically changed. The Ancestral Cascades were now composite cones and about as high as the Modern Cascades. As erosion deposited sands into the shallow sea that is now the Willamette Valley, the rocks that formed also include the fossilized shells of marine animals. This rock unit is known as the Scotts Mills Formation.

The Stone Shelter at Silver Falls State Park

The first of the two members of the Scotts Mills Formation which is buried about 1’300 feet below the South Falls Lodge and extends down another 650’ is the Marquam Member. This is the only rock unit in the park that has shells in it, like the shells you see in the rocks that were used to build the Stone Shelter near the South Falls Lodge. If you happen to pass by this building, leave the fossils in the rocks for future generations to enjoy. During the 2 million years that this member was being created, Silver Falls State Park might have been at the latitude of Bandon, Oregon today. In fact, Bandon is a great example of what Silver Falls State Park might have looked like. Sticking out of the storm-torn beaches were rocky headlands from the Little Butte Formation. Varieties of shellfish are preserved in these rocks and reflect a warm, subtropical to temperate climate.

By 30 million years ago, the Coast Range began to rise out of the sea, and the Willamette Valley became an enormous marine bay similar to Puget Sound today. Silver Falls State Park was still sitting on the edge of the sea, but the deposition of sediments would push the coastline away toward the west. The environment of Silver Falls State Park would have been similar to that of the Seattle area before settlers found the area, but warmer. Various marine life including starfish, sand dollars, crabs, and sharks lived in this marine bay. At about this time, the marine bay was beginning to fill in from the south, near Eugene, to the north, near Portland.

As the coastline retreated away from the Silver Falls area, sand dunes dominated the area much like the Oregon Sand Dunes Recreational Area near Florence looks like today. An 800 feet thick unit, known as the Abiqua Member, was deposited from 30 million years ago to about 27.5 million years ago. This unit is located 500’ below the South Falls Lodge; it also can be found in the northwestern corner of Silver Falls State Park where presently there are no trails to allow park visitors to see it. The fossils in the John Day Fossil Beds represent the flora and fauna at this time. The Abiqua member took 2.5 million years to form. It was created from 30 million years ago to 27.5 million years ago and was later buried by another unit or two that have been completely eroded in the surrounding region.

By 24 million years ago, the Willamette Valley was created, and the Coast range would have risen out of the sea. A broad, flat plain where trees were being replaced by grass stretched from the Ancestral Cascades to the present-day shoreline. Lakes and ponds filled in any depressions until sometime between 24 and 16 million years ago when the Willamette Valley and Coast Range was folded like rumpled blanket. The sediments in the region of Silver Creek were tilted slightly to the east due to the Waldo Fault that underlies the Waldo hills between this park and Salem, Oregon. Any layers of rock from 27.5 million years ago to 16.5 million years ago have been completely eroded away in the region surrounding Silver Falls State Park, and is therefore interpreted to be eroded away beneath the park.

The second part of the series is here: The Story of Silver Falls State Park--Part 2