Unearthing secrets buried beneath Tiger Mountain
June 29, 2010
By Chantelle Lusebrink
With paragliding, wildlife galore and nearly 80 miles of trails, Tiger Mountain State Forest is a community treasure for not just Issaquah, but for residents living in the greater Seattle area.
But some of Tiger Mountain’s most unique treasures are the ones that lie beneath the ground.
A history of uniqueness
The Issaquah Alps themselves are unique.
Tim Walsh, geologist with the state Department of Natural Resources, holds the fossil imprint of marine life from 45 million years ago on Tiger Mountain. By Greg Farrar
“In general it is an east-west trending chain of mountains that are riding the back of an east-west fault that is active,” Tim Walsh, a geologist with the state Department of Natural Resources, said during a trip to the mountain.
The Issaquah Alps stretch from Cougar Mountain in the west to Rattlesnake Mountain in the east, and have been part of extensive studies for many years. But recently, they are getting more attention.
New technology is enabling geologists to take a much closer look at the mountains than ever before. Peeling back vegetation, lakes and other human developments with radar technology, geologists are able to accurately map the area and confirm what they’ve long suspected is part of the region’s active faults.
The new maps will enable geologists and state officials to better understand how the active faults are shaping our region, said Joe Dragovich, a geologist with the state Department of Natural Resources.
Unlike the barren lands of California along the San Andreas Fault, the vegetation of the Pacific Northwest has made it nearly impossible to see how the Issaquah Alps connect into the South Whidbey and Seattle faults that are active, he said. But today, they are making great strides.
“As a land formation, that whole area is part of the Seattle uplift. That’s interesting,” he said, adding that it also borders the Whidbey Fault to make it an active earthquake area. “It’s an example of plate tectonics in action.”
The information will help geologists and state officials understand what areas are prone to earthquakes and what repercussions a large quake may have for surrounding communities, he said.
By taking a six-mile hike to the 15 Mile Creek Trail gorge, you can see what an active fault is doing to the mountain’s geology.
Once there, you’ll see how the exposed gorge walls take on color striations similar to a sunset. Millions of years of soil deposits from glacial formations and changing climates are inscribed in them, layer upon layer.
Where a belt of specifically colored soil dips drastically and continues in a straight line again, you are more than likely looking at the work of an active fault, Walsh said, pointing to two instances on the gorge walls above the swift creek.
Amber
A few hundred feet away, before you get to the 15 Mile Creek gorge outlook, there is a fork in the trail. At the end of the upper fork, be ready to use your eyes and exercise patience. To find small globules of amber on Tiger, you’ll need both.
Amber was discovered on Tiger during its mining days, in the early 20th century, Walsh said. Amber is popular as a semi-precious stone in jewelry.
Cougar Mountain was the most well-known location of coal mining in the Issaquah Alps, but there are plentiful deposits on Tiger, too. You can see the remnants of foundations for crushers, railroad ties for mining carts and locomotives, and even a sealed coalmine while walking along the trail.
The mines on Tiger, however, never saw their full operational potential. The way the coal seam formed geologically made it difficult to extract coal. The creek gorge cut through the center of one of Tiger’s largest deposits, making it difficult and expensive to mine, Walsh said.
You might be surprised to learn that Tiger Mountain was once part of a vast delta plain that extended from Idaho to the coast, with meandering rivers during the mid-Eocene years, about 50 million to 45 million years ago, said George Mustoe, a research technician for Western Washington University’s geology department.
Mustoe spent time at Tiger Mountain studying its amber deposits in the 1980s.
“The climate in this region was sub tropical, so the vegetation was very different from what we know today. In fact, there were plants that we would consider modern relatives of plants that live in Asia and Central America,” he said. “The amber is a really interesting story, because it is the resin from trees, and woody trees at that. It is nature’s Band-Aid.
“For a tree to drip resin, it’s like a person bleeding, in that it takes energy and you lose a vital resource, so something must have allowed for the accumulation of resin to occur.”
The resin, Mustoe said, most likely came from a Metasequoia, a tree that many in the scientific community thought was extinct until recently. The tree has large, sticky feathery needles that dropped each fall like a deciduous tree and regrew them in the spring, Mustoe said.
You can find the amber at the top of the fork in the upper path and roughly 60 feet up a fairly steep hillside. To unearth it, you’ll need to take samples from the coal seam at the top of the hillside and below a grouping of trees.
After taking a piece from the seam, break it open several times and look for nearly transparent red, orange and brown pieces of amber, often no bigger than a small fingernail.
Fossils
Another fun family adventure allows you to get dirty and dig in at one of Tiger’s several fossil locations.
As surprising as a subtropic forest may have been, imagine Tiger Mountain with large marine embayments, Walsh said.
“They are kind of enigmatic fossils,” he said. “To our best knowledge, it was lower here, so it flooded with marine water or there was a finger outlet here that allowed the marine water to pool.”
Roughly 45 million years ago, during the middle Eocene period, marine life thrived in sea waters where Tiger Mountain stands. You can see them still in the mud and sandstone rocks and hardened sediments making up parts of the mountain.
Echinoderms, gastropods, pelecypods and scaphopods were among the species that called the embayments home. Today, we’d know them best as sea urchins, sea snails and slugs, clams and mollusks.
The easiest trail to access a fossil site from is a state logging road, located off state Route 18 as you head west. About a mile or so from the highway summit, you’ll see the road, blocked by a blue gate, on your right hand side. You can’t take your vehicle in, but you can park near the gate and walk or bike in about a half-mile to the last high voltage power pole, which sits on the road’s first plateau.
Bring your camera, as the views of the Cascades and of North Bend from the site are spectacular.
About 50 yards up the hill to the left of the roadway, there is a standing outcrop of exposed rocks. Make sure you expose a new rock surface, as areas that are fractured have likely been damaged by the weather and the fossil imprints have more than likely been eroded away by the elements, Walsh said.
You can use another piece of mudstone and gently chisel pieces off the face to expose the surface.
With a sharp eye and about 10 minutes, you can easily find a fossil imprint.
Looking at a small clam-like imprint, Walsh pointed to the ridges on the shell and where it connected. Most of the time, you won’t actually see the critter itself, he said.
“Those are long gone, but you do see where they were clearly,” he added.
Whatever geology adventure you choose, you won’t be disappointed at Tiger Mountain.
“We talk about traveling all the time. What we don’t talk about so much is the idea of time traveling in the area we live in, wherever it is,” Mustoe said. “Amber and fossils are the closest things we have to a time machine.
“When you look at a rock or see a dried up tree globule, you get a glimpse of the world we live in and how it looked 45 million years ago. How cool is that?”
Getting there
Amber and coal
Access the trail system through the state Route 18 summit at Tiger Mountain. The logging road to the trail is gated, so you will want to ride a bike or hike to the trailhead. Take the 15 Mile Creek Trail Head, about five miles up the logging road. Bicycles aren’t allowed on the trail, but there is a lock-up area to keep them safe. The 15 Mile Creek Trail is roughly one mile, well-maintained and fairly flat. At the fork in the trail, take the higher trail to the coal seam and amber outcrop. The amber is in the coal and rocks up a steep incline and below a grouping of trees. Use tools to dig into the seam and break apart the rocks. The globules of amber are orange, red and brown, and are typically the size of a fingernail.
Fossils
The easiest site to access on Tiger Mountain is from state Route 18 west. About a mile from the highway summit, turn right onto a logging road. The road is closed to traffic, but you can park near the gate and walk to the site.
General rules
Tiger Mountain State Forest is owned by the state Department of Natural Resources. It is a working forest, and money collected from logging and mineral sales goes toward the state’s public schools trust. Therefore, anything found onsite is the state’s property.
Under no circumstances is money to be made from the sale of minerals, stones or fossils, or money to be made from leading tours on public lands.
“‘Casual Use’ activities causing only negligible disturbance (such as hand sample collection) are allowed on most public lands without advance notifications,” according to the 2009 edition of the Gold and Fish Pamphlet from the state Department of Fish and Wildlife.
On the Web
Check out the state Department of Natural Resources’ website and the Department of Fish and Wildlife’s website.
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