Every Place Has a Story: Prichard, Oregon's Smallest State Park

I've been visiting Florence, Oregon for a number of years, and it is a beautiful place. The Siuslaw River reaches the sea near the town and at the northern edge of the Oregon Dunes National Recreation Area. Sea Lion Caves lie hidden in the coastal cliffs just north of town. But Florence holds one other distinction: it has Oregon's smallest state park. It's called Prichard State Wayside, and it totals an entire 0.5 acres. To be sure, Prichard is not the smallest park in Oregon. That distinction belongs to a city park in Portland called Mills End Park. It's located at in intersection in the city, and has a total area of 452 square inches.

A visit to Prichard State Park is not exactly a life-changing event. The half acre includes a grassy swale, a couple of trees, a small parking area, and no facilities at all. There's a single sign identifying the site. There's no interpretive signage, and little information on the internet about the history or genesis of the park. I'm guessing it was some land that was donated to the state, and the officials that be couldn't really decide what to do with it.

Looking at the park, I was reminded of something that I tell my students on the opening day of every class: geology is where you find it, and every place you find has a geological story. At first glance I was hard put to imagine an interesting geological story for this place. But a moment's reflection proved the opposite.

Let's take a look at the setting of the park. It is a grassy slope that is situated along the Siuslaw River, which from this angle looks like a huge body of water. But it isn't technically a river. It's a tidal estuary, and the wide body of water flows either downstream towards the sea or upstream in response to the daily tides. In a few hours the entire mudflat in these pictures will be covered with water. The area of tidal influence extends 26 miles inland, which is nearly 20% of the entire length of the river. Upstream of the tidal influence, the river is modest, with an average flow of about 2,000 cubic feet per second. That's less than a third of the more familiar Rogue River.

The story of any part of the Earth starts with the rocks that underlie the site. A quick look at the geological map of the park region shows that the "bedrock" is composed of "Qal", translated as 'Quaternary alluvium". Alluvium is our term for any of the loose sediment that covers the more solid rock underneath. "Quaternary" is the last little gasp of geologic time, encompassing the last 2 million years. The unit might include the mud of the estuary, river and or gravel, or dune sand. The Qal at Prichard is most likely slightly consolidated dune sands, which is a material that underlies most of the coastal areas in the vicinity of Florence. Sand carried along the coast by wave transport is blown inland by persistent onshore winds, forming the dunes for which Oregon Dunes National Recreation Area is justly famous.

The picture above shows the coastline just north of Florence. The region has undergone a significant change in the last hundred years or so. Migrating dunes can certainly be a problem in developed areas, so a European species of beach grass was introduced in the 1920s in an effort to stabilize the dunes. The grass worked too well, and sand has been trapped in the area adjacent to the shoreline, building into an ever higher ridge of grass-covered sand. The area inland has been starved of sand, so it has blown farther inland, leaving a low area called the deflation plain, a region now covered by small ponds and scrubby forests.

Sand is a famously unstable foundation for buildings (it's even in the Bible), but dunes that have been stable for centuries or millennia will sometimes be consolidated by calcium carbonate or other minerals in the groundwater. That is a much firmer surface to work with, and thus the development of the Florence area has been possible.

Going back in geological time often leads to strange changes in the appearance of the landscape. For instance, during the ice ages of the last 2 million years this little park would have looked far, far different than it does today. It's not because there was any ice; the glaciers that were present in Oregon were many miles away up in the Cascades. The big different was sea level. With so much ice locked up in the vast continental glaciers that covered almost all of Canada and northern Europe, sea level dropped to around 300-400 feet lower than today. Prichard State Park a few tens of thousands of years ago would have been perched on a terrace above a Siuslaw River ensconced in a deep river gorge hundreds of feet below. The outlet of the river would have been miles to the west of where it is today. 

One last aspect of the geology of any region is how it affects those who live there. Hazards present at Prichard would clearly include flooding and fires (especially in a time of global climate change). As noted earlier, the average flow of the Siuslaw River is about 2,000 cubic feet per second. The record flood on the river was around 45,000 cfs, and in that circumstance, the water would rise to inundate the little park.

The other very serious threat is that of tsunamis. These destructive surges of water could be developed by a massive earthquake on the Cascadia Subduction Zone that runs parallel to the coast. A quake has now been documented as having reached magnitude 9 in 1700. Such an earthquake is thirty times more powerful than the magnitude 8 quake that devastated San Francisco in 1906, and around a thousand times more powerful than the 1988 Loma Prieta earthquake (just short of magnitude 7). Tsunamis can also be generated thousands of miles away in places like Japan or Alaska. Whether local or distant, Prichard State Park would be a dangerous spot if a tsunami ever hit. There would be no "breaking wave" as is shown in many photoshopped images. The water instead arrives as a surge moving rapidly upstream at high speed. In moments, the park would be inundated to a depth of several tens of feet. The water would eventually recede, but then a second, third, and maybe fourth wave will follow.

Geology is everywhere, and everywhere has a geologic story, even Oregon's smallest state park. Check it out, if you can find it!

That's a Huge River! Well, Not Exactly...Sediments in the Siuslaw River Estuary

In the photo above we're on a hill overlooking the Siuslaw River near Florence, Oregon. From this point of view the river looks huge and indeed the channel is navigable and leads to a working marina a mile or two upstream. But looks can be deceiving, and a careful observer will note that the "river" spends half of the time flowing the wrong direction. Like two of the last posts here on Geotripper, the Moon is part of the story...this is a tidal estuary. The Moon has the greatest influence on the intensity of the tides.

There is a Siuslaw River, of course, but it is just not quite this big. It is 120 miles long, starting at an elevation of 636 feet in the Oregon Coast Ranges, draining an area of about 773 square miles. The discharge of the river varies greatly depending on the season. The long-term average is around 3,000 cubic feet per second, but last week when I was there it was a mere 145 cubic feet per second. During the worst of flooding the river can exceed 50,000 cfs. But it is the lower part of the river that is affected most by the tides. During extreme high tides, changes in river level can be noted 26 miles upstream.

An estuary is the portion of a river influenced by tides where there is a constant mixing of salt and fresh water. Estuaries are rich in nutrients and one of the richest biomass producers on the planet. The estuary of the Siuslaw River developed at the end of the last Ice Age. With so much water locked up in glacial ice, sea level was hundreds of feet lower than it is today, and the Siuslaw River occupied a deep channel that continued for miles west of the current coastline. As the ice melted, sea level rose and flooded the river valley, but the Siuslaw River carried vast amounts of sediment to fill the flooded channel, forming the flat level valley we can see today. Additional sediment is added by wind blowing sand from the coastal dunes that line the lower channel (the Siuslaw is at the northern end of Oregon Dunes National Recreational Area).

When I was there a week or two ago, we experienced an intense low tide that exposed some rarely seen sedimentary structures in the channel. When the tides rise, water rushes upstream, and when the tides fall, the water goes out to sea. Flowing over the loose silt and sand, the flow causes the development of gigantic ripples like those in the pictures above and below.

It didn't occur to me at the time, but this is not a natural channel. Because of the ship traffic, the channel is dredged to maintain sufficient depth for the boats to pass through. There are other changes in the last century. The drainage of the Siuslaw is one of the most heavily logged regions in Oregon, and the clearcutting of timber has changed the nature of slope failure and flooding on the river. Trees and logjams used to trap sediment upstream, providing a rich breeding ground for salmon. The logjams were removed and the river scoured the channel to bedrock in many places. One of the most destructive activities was the process of "splash-dam" logging. Temporary dams were built across the river and trees were cut and floated in the reservoir. The reservoir was then dynamited and the resulting flood carried the logs downstream to the mills. The practice, needless to say, was hugely destructive of the salmon fisheries. Over the years the salmon runs declined from hundreds of thousands of fish each year to mere thousands.

Some of the sources I checked pointed out that the Siuslaw once was the second richest salmon fishery in Oregon after the Columbia River. Efforts are being made to improve the environment to build the salmon runs. They'll never be what they were a century ago given the vast changes upstream, but there is a lot of potential for growth of fish populations. In the meantime, it is an interesting place to visit if you are ever lucky enough to find yourself on the central Oregon coast (especially during the present heat wave!).

Just a Beautiful Sunset, and Maybe a BIt of a Green Flash...

The gloom and the rain cleared out for our last night in Oregon, and we were treated to a gorgeous sunset. We had a clear horizon to the west, so as usual I tried to catch (maybe) a bit of the green flash.

The green flash is a somewhat rarely seen spectral phenomenon that occurs the moment the sun disappears below the horizon. Light from the sun is being refracted through the atmosphere, and at sunset the last of the spectral colors to appear is green (and sometimes blue). The effect only lasts for a second or two, so I'm never quite sure what I've seen. I just trust the camera to catch the effect, to varying success. 

My previous try was more convincing, but I see a bit of green in the picture below. You're welcome to tell me what you think!

The Green Flash, the Green Rim, and Coastal Sunsets

I'm in a beautiful place, no doubt about it. I'm in central Oregon on the Siuslaw River visiting for the holidays, exploring new terrain that I've never really seen before. Luckily, we have the time to linger for a few days instead of rushing home, so it actually feels right to sit on the porch and just enjoy life and my relatives (whom I love spending time with).

And what a porch! I took advantage of clearing skies to watch the sun set tonight. I've got the new camera and I am still learning its capabilities, so I decided to catch the whole drama of the sun disappearing below the distant horizon. I also hoped to catch the legendary "green flash", which I have never seen (despite my hopes in previous posts).

I probably still haven't seen it, but I was reading about these things, and noted that a "green rim" can sometimes be seen as well. If my camera is delivering true colors, I think I captured the green rim at the very least, across the top of the disk of the sun.

 The green flash is a sudden flash of greenish light above the sun at the moment of sunset, and it is said to last only a second or so. As the sun dips into the horizon, the layers of the atmosphere will cause some of the sunlight to be refracted, with red and orange on the lower parts of the disk along with green (and rarely blue) across the top.

If I caught the flash at all, it was probably here, as this was the only green I could see while I was snapping the pictures. I leave it to the judgement of those out there who have seen the green flash before as to what I caught this evening. I welcome your thoughts and observations!

Happy Holidays from Geotripper!

It's a big beautiful world out there, and all I can think of for this day is to share a little corner of it with you all, and to wish you all a happy and safe holiday season in all your travels and visits. We've enjoyed a few days along the central Oregon coast, and now we are setting off on the homeward journey (through a rather exciting looking storm!).

The Siuslaw is one of the many rivers that flow out of the Oregon Coast Ranges to the sea. At Florence, the river flows through the Oregon Dunes, and the mouth of the river is the site of a constant battle between river, dunes, and waves.

The bridges of the Oregon Coast are beautiful, and from underneath some recall the ruins of Gothic cathedrals.

We didn't see a lot of sun during our visit (Really? It rains in Oregon?), but it peeked out for a beautiful sunset the other day.

For Christmas Eve, we explored along the coast a bit and found a beautiful spot where Cape Creek meets the sea at Heceta Head. There's a lighthouse hidden in the trees above the center of the photo.

Have a great holiday! Peace to all.