Yup. We finally made it to the actual geology of Discovery Park. Be amazed. Be very amazed.
I don’t remember seeing South Bluff the first time I esplored, way back in 2000. I’d abandoned my best friend to the vicissitudes of the big city, because he’d decided after our stint at Ravenna Park that he’d had enough of nature, thankseversomuch, and desired the wilds of a two-story Barnes and Noble. I handed him the keys to the rental car, hopped a bus, and headed off to do me research. I’d set an important scene at Discovery Park, y’see, and spent my time there busily trying to find locations that matched what I needed. I did make it down to the beach, but all I remember from that excursion was the lighthouse, the washed-up jellyfish, and the baby seal – my first! – that posed so prettily for me. I didn’t make it much further than the point – had to get back up the hill and catch the bus back to the hotel.
So the first time I saw this:
Geologists in the audience may begin salivating… now.
I spent quite a bit of time with that bluff that sunny afternoon, long enough for the sunlight reflecting from both water and cliff to burn me a nice bright red. I remember patting it, delighted with its patterns, the stolid solidness of it. I’d seen the signs up top saying it was unstable, but it was hard to believe them at the time. Sure, people could (and unfortunately did) carve all sorts of nonsense into it, but then, they did the same thing to the lithified dunes around Page, so it didn’t occur to me I wasn’t looking at rock so much as a coulda-been-rock-someday. I’m not used to what amounts to mud forming a vertical cliff, y’see. First bluff I’d ever seen in my life.
Click to embiggen that photo. Take a closer look at it. Note the trees around its shoulders. See how they lean every-which-way? See how young they are? This is our first hint that the “unstable bluff” signs weren’t lying. Those trees occasionally get to take the ride of their young lives as the slopes below them go merrily slip-sliding into the sea. Then they add to the driftwood population in Puget Sound.
Hard to believe you’re looking at a glacial landform, innit? Allow me to show you it:
So this one time, before the Cordilleran Ice Sheet, there was this floodplain. Puget Sound wasn’t so much as a gleam in a glacier’s ice back then, although the ice was gathering itself up in British Columbia and getting ready to make a run for the border. What I’m playing Vanna with up above was laid down in warm climes between 22,400 and 18,400 years ago during a time known as the Olympia non-glacial stage. When Canada next goes under the ice sheet, it appears we’ll have a while longer to enjoy our pleasant marine climate before we, also, are covered under several thousand feet of ice. Woot! Suck it, Canada!
It’s really lovely stuff. Look at the pretty patterns:
This stuff is hard. When you pat it (yes, I pat rocks, you gotta problem with that?), it gives you a nice solid sandstony feel. It’s not rock yet, but it’s certainly headed that way – some bits more than others:
This gives you a good view of what you’re dealing with – some bits are more sandy, some more silty, even though it’s weathered to a nearly uniform color. Some bits are harder than others, and resisting erosion a little more successfully. But I’ve got bad news for it. The waves that lap up against the bluff at high tide are cutting the ground right out from under it:
Oh, yes, indeed: a nice, smooth curve carved into the wanna-be rocks, which is just an invitation to gravity. The bluffs are eroding away at the rate of around 80 feet per century. Eventually, the Visitors Center’s gonna have a nice Sound-front view. Elsewhere, some homeowners have already seen their property values decline right into the sea. You want long-term stability, don’t build on a bluff.
And if you think that’s some impressive wave-action, check out the cave carved round the other side:
So, dear Olympia non-glacial stage sediments, this is your fate:
One day, the waves are going to cut your feet from under you, and gravity shall make sure you have a nice day on the beach, where you shall be resurrected as sand, perhaps one day to rise as a bluff once more.
By now, my darlings, you might have noticed the lovely wavy patterns in all these photos. Movement on the Seattle Fault may have something to do with it; so could ancient landsliding and that bloody great 3,000-foot thick glacier sliding over it. Things that start out all straight and neat in nature routinely end up crinkled, just like my laundry.
Speaking of faults, I think I found a small one, and it’s not merely my personal fault of not using a damned iron. The experts can tell us if I’m right:
Could just be funky erosion, I suppose – there’s not much offset that I can see – but it could also be a baby fault saying, “Oh, hey, I’m not-quite-lithified sediment, and there’s a shit-ton of weight on me! Ow!”
And what, you may ask, is weighing so heavily upon our lovely Olympia non-glacial stage sediments, other than more Olympia non-glacial stage sediments? Why, that would be the Lawton Clay! Here’s a shot stitched together by my intrepid companion, a slightly larger version of the sea-cave shot above, showing the Lawton Clay bearing down upon our poor, innocent Olympia non-glacial etc:
The Lawton Clay is that forboding dark-gray stuff, although bits of it seem to have weathered white up there. The Lawton’s got calcerous concretions and vivianite in it, some of which might provide those chalky-looking patches (although from what I understand, vivianite’s only chalky white when it’s fresh). What you’re looking at up there is the footsteps of doom. You see, this stuff probably got laid down in a maclargehuge lake. And the reason for a lake being there is, the Puget Lobe of the advancing Cordilleran Ice Sheet had blocked the northward-flowing rivers that drained out the Strait of Juan de Fuca at the time. It came closer, and closer, and…. left us with a slippery slope, that’s what. Because, you see, the Lawton Clay likes to fall down and go boom. See, I can prove it to you:
We found chunks of it all over the place. And ’tis indeed clay – you could practically make pots with it. Should you find yourself on the beach there, go ahead and pick some up. You can chunk off bits quite easily and moosh them in your fingers. Look, some of it’s even pre-chunked for you:
You might notice this clay’s rather prone to fragmentation. And anyone who’s dealt with clay knows how slippery it gets when wet. Now consider that a good part of the bluff’s trying to balance on it, and, well, you know – stuff happens:
Big part of the cliff fell down and went boom. For some inexplicable reason, probably having to do with playing with clay, then photographing clay, then realizing “Oh, fuck, the tide’s gonna eat me if I don’t move!” I didn’t get a full-length view of the slide, but the above is the nice scarp, and down below here you can also see a nice clean shoulder of (probably bloody annoyed) Olympia etc., and then the very top of the talus slope formed by the slide:
Respectable little landslide, that. Wasn’t there last time I visited, and might not be there when I go back. That’s the nature of the bluff. It’s like a Thanksgiving turkey that nature keeps carving more bits off of.
When you get to the very tip-top of the bluff, you’ll see that the glacial story didn’t end at a bloody great lake depositing clay all over the place. No, indeed. You’ll find the Esperance Sand, a nice thick bit of glacial outwash deposited by meltwater streams flowing merrily south as the Puget Lobe advanced on Seattle with the coldest of intent. There aren’t hugely good exposures from this angle at South Bluff – at least, not with the incoming tide driving you right against the cliff – but I do believe this is a nice bit of it:
The Esperance Sand is, indeed, lots of sand and silt. It got draped all over the landscape right around 18,000 and 15,500 years ago, before the glacier caught up to it and buried everything under a nice coating of thick, heavy Vashon Till. A lot of that till has eroded away near the Sound here in Discovery Park, but there are still places where you can see it. You’ll know it when you encounter it: it’s hard, weighty, dark-gray stuff filled with rocks. In places, it’ll be overlain by yet more fluvial deposits left by yet more meltwater streams as the 3,000 foot ice sheet saw Olympia, said “I came, I saw, I’ve bloody well conquered enough of America, thankyooverymuch,” and headed back for Canada.
One thing I’m pretty sure most people don’t realize as they explore the nice, sandy, somewhat duney meadows atop South Bluff is that all this nice sand has nothing to do with the sea. The sea wasn’t even there for a very long time, and when it was, didn’t hit the top of the bluffs. No, that’s all stream work.
Amazing, innit? So take a good, long look at ye olde bluff, because while it has a long and busy past, it’s got a short present and a non-existent future:
Tip o’ the shot glass to the Hiking Guide to Washington Geology and Landslides and Engineering Geology of the Seattle, Washington Area, without whom this post would’ve been impossible.