NELL/S CANYON

 

The culmination of our rock-intensive tour of Washington was an all-day trip in Hells Canyon by jet boat; It was loads of fun.  Hells Canyon is carved by the Snake River into gradually uplifting terrain near the common meeting point of Washington, Oregon and Idaho.  Our boat leaves from Clarkston, Washington.  This uplift and erosion has resulted in a canyon deeper than the Grand Canyon, though it is fair to say, not nearly as majestic.  The cause of the uplift is not certainly known, although I imagine it had something to do with migration of North America across the Yellowstone hotspot.  But, hell, that can’t be right; canyon-cutting began only six million years ago.  Oh, well. . . .

The lower part of the trip cuts through Columbia Plateau Basalts.  The valley there is wide, with lots of human habitation.  Further upstream it narrows and has only a few scattered ranches to mark the presence of humankind.  There it is cutting through ~ 300 Ma rocks of an accreted terrane; in this case volcanic rocks overlain by limestone.  These rocks formed somewhere west of North America, in an ocean basin, and were scooped up by that continent as it moved relatively westward.

Much of western North America is composed of such terranes.  They often are referred to as “exotic terranes”, but I much prefer “accreted”; to me, “exotic” brings to mind some nubile lass dancing, clad only in a pair of fans.  Not that I have ever seen such, of course.

So, it was a great trip.  I highly recommend getting out into the geomorphic wonders of central and eastern Washington.  But maybe when it’s a bit cooler.