Our story begins the night before the trip, as I was trying and failing to find anything on the geology of Franklin Falls, and cogitating about what I remembered seeing there oh so long ago. I’ve had a few samples sitting on a side table for years, and occasionally, I’d take them out and turn them over in my fingers and ponder. They seemed sedimentary, but also volcanic. They might have been sandstone and slate, only they were super-hard, and made strange sounds. I went round and round with them. Andesite? Bizarre basalt? Whut?
Then, last night, I began pondering the fact that the Snoqualmie Batholith is right there. The South Fork Snoqualmie River flows over it near the road. And you can find exposures of that grand granodiorite along the bits of the river beneath the gorge. I’ve played there, in fact. I began thinking relationships. I thought of other places where I’ve seen igneous rocks intrude. I thought of going up on Marys Peak with Lockwood, and looking at the gabbro sills, and then that trip down to the hornfels, which is what happened to sandstone when the adjacent magma baked it.
Obvious, now that I think about it (after being trained up by Lockwood). The magma of the Snoqualmie Batholith would have heated the country rock up to a nice altering temperature. It would have baked everything around it. So of course, there would be a good section of hornfels, right? And now I thought about it, the stuff I’d collected looked and sounded like thoroughly-baked hornfels. It has a rather distinctive ring, as you might notice if you watch the video of Lockwood whacking at some at this link. Its presence would fit with the skarn found along Denny Creek. It would explain the odd appearance of the rocks, and their remarkable hardness, and the way they break in rather stark geometric lines. So I now had a theory, and I could test it when we got there. I did, and now I’m damned sure it’s hornfels.
I was eventually able to locate something of a geologic guide (pdf) that confirmed my observations, so that’s outstanding. Lockwood hasn’t been pounding geology into my brain for three years in vain. I can now go to areas where I don’t have anything but the vaguest idea of what’s there, observe the bits, and fit them together into something of a coherent story. I’m starting to Figure Shit Out. And then I can say to B the fact that precious metals and such like are often found round batholiths, and then glance at a geologic diagram of the area in Roadside Geology of Washington and not be in the least surprised when it turns out there’s gold in them thar mountains.
Also was able to recognize a lot of glacial features, like U-shaped valleys and moraines and horns and suchlike. Upshot: pal around with geologists long enough, and you’ll be able to start figuring it out on your own.
Other important things realized:
1. Even in June in a part of the Cascades relatively low in elevation (2600ft), you’d best be prepared for snow:
We never did get cold until we were coated in spray from the falls, but there were plenty o’ patches o’ snow, and the path was sopping wet from where some had melted in many places, and in some places, you actually had to walk on snow because it hadn’t melted yet. Stuff like this still blows my Arizona mind.
2. If you put your trail beside a river bank, you’d best be prepared to have bits of it eaten by the river.
3. If you go hiking on a trail the snow’s only just melting off of, the volunteers probably haven’t had a chance to go at it with a chainsaw yet, and you’d better be good at crawling over fallen trees:
4. And B is a fantastic adventuring companion. I knew that already, but I know it even more now.
This was a fruitful trip. Not only is there enough geology to keep us busy for at least one more post (after I’ve had a chance to brush up on certain details of it), I’ve got a huge amount of skunk cabbage, some mystery flowers, some not-quite-mystery-flowers, some cryptopods (one of which is going to delight you: it’s like the Jaws of the insect world), some very awesome fungi, moss and lichen that have turned some rocks into the Wicked Witch of the West, some mystery botany, lots of stuff for a discussion of old growth trees, large woody debris, more waterfalls… at this rate, I’m going to have to start posting about sixteen times a day to catch up with the backlog of stuff.
So I’m going to try to get the geology of Franklin Falls posted tomorrow, and I might hit you with a cryptopod or two. And didn’t a few of you want Marys Peak lilies? I’ve got ‘em ready to write up. Stay tuned!
What’s that? You can’t wait for a photo of the falls? Well, all righty, then. I’d hate to make you suffer.
Much more to come, my darlings, I promise!