|Grande Ronde Silhouette|
The character of the place changes a bit down here. And it's a good place to talk about basalt.
First off, if one's just taking a casual look round, it's easy to be deceived. What with all these dikes, stringers, sills, and so forth, it's easy to think that these basalts are natives. In fact, for a while, that's just what geologists thought. The source didn't seem like it could be too far from here. After all, the way the Columbia River Basalts insinuated themselves into the local strata, it looked just like they'd arrived from below.
However, that's not what gravity and chemistry tells us.
|A Finger o' Basalt|
But then came chemistry. And chemical analysis said, "Yup, that's sure Columbia River Basalt, that is. Eye-din-tee-cull." It boggles the mind - we've had zero experience with state-spanning flows of flood basalts in recent history. If I'm remembering rightly, humans in historical time never have witnessed such a thing. But it happened here.
Down here to the south, the Grande Ronde looms more. And it's a mass of fractures and fragments, welded together.
Clamber over the riot of rocks, basalt rising up on both sides of you. Once you're through the gap between head and stack, you'll suddenly emerge from igneous to sedimentary again.
Down near the tide line, when you can find bits that aren't all covered in crunchy-coated biology, you can see just how smooth and slick basalt can become when polished by sand-laden waves.
Things look rather different where the water's been at the sandstone.
I want to turn your attention now to the head, where you can see basalt and sediments getting really intimate.
|Jaunty Basalt Cap|
In places, the intruding Grande Ronde squirted up through the sediments. Remnants still stand watch, tall and imposing.
Come closer still.
Ye olde indispensable volumes of reference as the author was trying to make sense of it all:
Fires, Faults and Floods - one of the best roadside guides to the Columbia River Basin evah.
In Search of Ancient Oregon - simply the most beautiful book written about Oregon's natural history.
Hiking Oregon's Geology - chock full o' adventurous goodness sure to help you get your rocks on.
Northwest Exposures - tying the whole shebang together in one easy-to-follow narrative.
Cataclysms on the Columbia - the book that truly helped me comprehend the incomprehensible.
The Restless Northwest - short, sweet, and yet comprehensive guide to Northwest geological shenanigans.
Roadside Geology of Oregon and Roadside Geology of Washington - indispensable references and inspirations.
Glacial Lake Missoula and its Humongous Floods - not only an informative guide to the discovery and history of the Floods, but an apt title, too!