21 February 2011

Mount Washington 1

Posted by Callan Bentley

I’d like to start a series on the geology I encountered last summer at Mount Washington, in New Hampshire. It’s not only the site of the “World’s Worst Weather,” but it’s got some cool rocks and some cool geomorphology too. I hiked it last August with my fiancee Lily, and my cousin Brad. Lily and I got to the mountain first, and to kill some time while we waited for Brad to drive up, we checked out a prominent outcrop on the west side (east facing, hence the fine morning lighting) of the road up to Pinkham Notch.

According to the superb map accompanying Dykstra Eusden’s book The Presidential Range: Its Geologic History and Plate Tectonics, the outcrop we were checking out is the Crawford Member of the Rangely Formation, a gray migmatitic orthogneiss.

A quick taste of what we saw there:

Here’s a pegmatite dike dipping at (apparently) 45° to the north (right) and a big, gray, angular inclusion:

A closer look at a similar exposure, a bit further down the outcrop:

Again, you can see a big angular gray inclusion (this time above me), and also an elliptical inclusion (“concentrically mineralogically zoned calc-silicate granofels”) that’s tan in color. Let’s zoom in on that second one:

Nearby were some ground-level exposures of the pegmatite. For instance, consider this veritable “library” of muscovite books:

And here we go with a rust-stained exposure of pegmatite, bearing large black crystals of tourmaline (?):

More later, from the trail…