Painted Hills Unit of John Day Fossil Beds, photo from American Southwest

[Note: This entry was posted on Aug 22, 2019. It is backdated to keep it in chronological order.]

by George Taniwaki

While traveling to eastern Oregon to see the total solar eclipse (Real Numeracy Aug 2017), Sue and I also checked out some science under our feet, learning about the Cenozoic era. That’s the current geologic era, the past 65 million years since the dinosaurs became extinct and mammals and birds became plentiful.

Our solar system is over 4,800 million years old, so the Cenozoic era covers less than 1.5% of the total geologic history of the earth. The Cenozoic era is divided into 3 periods which are divided into 7 epochs.

In this blog post I’ll cover the landmarks we visited in geologic timeline order. They are not in the order we visited them, and we did not visit all of these sites during a single trip.


Geologic map of Washington State, Image from USGS

Paleocene—Volcanic ash at John Day

Driving south from the Columbia River along the John Day River, you will see well-defined stripes of gray, red, and yellow sandstones. The oldest of these sediments were laid down during the Paleocene epoch (not to be confused with the larger Paleogene period) 65 to 55 million years ago. The latest were laid down during the Miocene epoch 23 to 5 million years ago.

Large and small mammals, most now extinct, roamed the plains here. At different times, they included 3-toed horses, camels, elephants, sloths, oreodonts, and saber-toothed cats. You can see some great artist drawings here.

This was also a time of significant volcanic activity. Magma rising from the mantle circulated to the crust creating inclusions and volcanoes in a volcanic arc.

If you look closely at the layers of rocks along the John Day River, you will see interspersed are thin layers of harder volcanic ash and lava. By measuring the ratio of isotopes in the ash layer, one can date the eruption and thus the age of the fossils found in the layer. By comparing fossils in different layers, one can build a family tree of the species.

When the hard volcanic ash and lava erodes away, it exposes the softer sandstones below. Once exposed, wind and water carved the steep canyons you see, called badlands. To learn more about the fossils, volcanoes, and current wildlife of the region, stop at the Thomas Condon Paleontology and Visitor Center  at the Sheep Rock Unit of John Day Fossil Beds National Monument.

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The Thomas Condon Visitor Center and a working lab, Photos from National Park Service

Eocene—Coal seams near Seattle

When plants, especially trees, fall into anoxic water, they are less likely to decay. If they remain undisturbed and are then covered by sediment, they will remain preserved even when the water recedes. Continued sedimentation creates high temperatures and pressures, slowly converting the plant material into peat, lignite, and finally to coal. There are two types of coal, bituminous, which is soft and tar-like, and anthracite, which is hard and shiny. Fossils and amber can often be found in all of these deposits.

In the Eocene epoch, about 55 to 35 million years ago, the earth was warmer than it is now. The area around what is now Seattle was above sea level and covered with forests, though the ground was swampy and muddy. These are the perfect conditions for creating coal seams. (For more, see Wenachee Valley College, Lecture 8.)

Commercial quantities of bituminous coal were first discovered east of Lake Washington in the 1860s (HistoryLink Jan 2003). Prospectors created both open pit and shaft mines throughout the region and used horse-drawn wagons and barges to cross the lake and haul the coal to the port in Seattle. Most of the coal was then carried by steamship to San Francisco. In 1870, a rail line was built from Newcastle going south around the lake to Seattle. This significantly reduced transport costs and coal production boomed. One hundred years later, the industry was in decline. The last mine closed by 1975.

The main road through the town of Newcastle, which is named after the coal mining town in England, is Coal Creek Pkwy. Coal Creek itself runs through Cougar Mountain Regional Park. And near the northwest edge of the park there is the Ford Slope coal mine exhibit. It’s worth a stop and only a few miles from my house.

There are more coal mines at Flaming Geyser State Park near the town of Black Diamond (which is another coal reference). Unfortunately, the park’s name is a lot more exciting than the park itself. There are no flames and no geysers. The name flaming geyser refers to vents in the mines to release water and methane (natural gas). The gas was flared off to prevent explosions. Today the vents are capped with concrete and there is not much to see here except an interpretive display.

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Miners at Cougar Mountain, photo from Museum of History and Industry; A nonflaming nongeyser, photo from Washington State Parks

Pleistocene—Cone shaped volcanoes

Nearly all the cone shaped volcanoes in the North Cascades were formed during the Pleistocene epoch, 2.5 million to 125,000 years ago. This includes the two most famous volcanoes in the range, both near the Washington-Oregon border.

At 4392m (14,410 ft), Mt. Rainier is the tallest mountain in Washington and is visible from Seattle. Mt. Rainier National Park is big, but there are only two main roads, so can get congested in the summer.

The other, Mt. St. Helens, erupted on May 18, 1980. I remember watching the TV news in Denver that day. The north face of the mountain collapsed, creating a pyroclastic landslide that instantly killed thousands of trees along with lots of wildlife and 57 people. The landslide flooded Spirit Lake which caused a tsunami that overflowed onto the Toutle River.

The eruption ejected about 4 km3 of rock, dust, and ash into the air. The fallout caused heavy damage as up to 1m (3’) of abrasive dirt clogged streets, houses, cars, and farms in downwind communities. I also remember about 3 days later a layer of fine dust coating all the cars and windows in Denver, which is about 2,000km (1,200 miles) downwind from Mt. St. Helens.

Today the Mt. St. Helens National Volcanic Monument is a natural laboratory showing how an area changes after a volcanic eruption.

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Iconic view of conical Mt. Rainier from Green Lake Seattle, photo from Brian Overland; A conical Mt. St. Helens before the eruption, photo from USFS.

Pleistocene—Glacial moraine in my backyard

The Pleistocene epoch is also known as the ice age. Over the past 2.5 million years, the fluctuations of the earth’s temperature in the mid-latitudes were in a range nearer the freezing point of water, sometimes above and sometimes below. This caused the polar ice caps to repeatedly advance and recede. The ground in many parts of Washington and Oregon has been scoured and eroded by multiple passes of glaciers. (For more see Wenatchee Valley College, Lecture 2).

Glaciers are like very slow moving rivers. As they flow, they scour the soil and rocks and sometimes carry them downstream. The rocks become rounded, like river rocks and the soil is finely ground into rock flour. Deposits of this material are called moraines.

The current epoch, known as Holocene, is an interglacial period where the climate is slightly above the freezing point of water and the glaciers have mostly disappeared. There are only few glaciers left in Washington or Oregon, all high in the mountains. The North Cascade Glacier Climate Project has been collecting data on these glaciers since 2005.

However, evidence of past glaciation is all around. Just digging a simple hole in my backyard is a herculean task because the ground is so hard and rocky. However, the ground is not made of clay (phyllosilicates), instead it is rock flour made mostly of ground quartz.


Rainier glacier, photo from NCGCP; Rocks and soil in my backyard

Holocene—Lava tubes at Mt. St. Helens

Sometimes the lava on the outside of a flow cools and hardens while the lava in the interior remains hot and continues to flow. This leaves a cavity called a lava tube. The most famous lava tubes are on the island of Hawai’i. But they can occur with any volcano, even on the Moon, Venus, or Mars.

In Washington, there is a lava tube, called Ape Cave, south of Mt. St. Helens. It was formed during our current epoch, called the Holocene, which started 12,000 years ago. The cave was probably created about 2000 years ago and is about 4 km (2.5 mile) long.


Going bananas in Ape Cave, photo from Daily Nathan on Reddit

Holocene—Ice caves at Mt. Rainier

Glacier caves are formed when water flows through a glacier. The heat melts the ice, forming a cavity. The air acts as an insulator, keeping the cavity warmer than the surrounding ice. Eventually, the cavities merge, forming a system of caves. The caves are unstable and can quickly be created or destroyed as the glacier moves or collapses.

The Paradise Ice Caves at the base of Mt. Rainier were once a popular stop for tourists. They were first discovered in 1908. They disappeared in the 1940s and again in the 1990s due to glacial recession. Because of global warming, it is believed that the caves are unlikely to return again until the next cooling trend.


A lone ranger in Paradise Cave circa 1958, photo from National Park Service

Holocene—Nike Missile Site

Back at the top of Cougar Mountain (about 2 miles east of the Ford Slope coal mine) are the remains of a control site and launch silo that were part of the Nike anti-aircraft missile program, built in the 1950s during the cold war. It is one of several launch sites in and around Seattle. It was dismantled in the 1970s and there isn’t much left to see.

This is obviously not a geological landmark. But it is still worth a visit to contemplate that humans have the ability to cause the end of life on Earth as we know it.


Sign post to the end of days, Photo from Beautiful Washington

For more geology field trips, see Science field trip–Northern plains (Oct 2018) and Science field trip—Bay of Fundy (Jun 2012).