3 June 2016

Friday fold: Riggins, Idaho

Posted by Callan Bentley

There are some folds in this stunning west Idaho landscape. Perspective is looking toward the north, more or less. See if you can find them:
Link GigaPan by Callan Bentley

One example that will probably be obvious at first glance is this syncline/anticline pair, differentially weathered, with subvertical axial traces, and an apparently shallow plunge of the axes to the south:


A more subtly expressed example is on the hill to the east (left), where differential weathering reveals a “Z” fold outcrop pattern:


Here are two annotated versions of the initial GigaPan image, with the trace of the foliation of the Squaw Creek Schist traced out in yellow (and projected into the sky in black) and the axial surfaces of the folds sketched in using red:

Link Annotated GigaPan by Callan Bentley

Link Annotated GigaPan by Callan Bentley

The region (Riggins, Idaho) has smaller scale folding too: here are some cm-scale folds from just south of the Time Zone Bridge, north (downstream) of Riggins:

Example 1 (two perspectives):



Example 2 (two perspectives):



I visited Riggins the week before last on a GSA field trip (“Accretionary Tectonics of Western Idaho”) led by Keegan Schmidt, Reed Lewis, and Keith Gray. I’ve got plenty more photos to share from that trip… stay tuned!