Ptygmatic folds in gneiss.
Ptygmatic folds are those which show high amplitude to wavelength ratios--and so often take on highly irregular shapes. They form where a relatively small proportion of the deforming rock is significantly more competent than the rest of the rock --in this case, the lighter-colored feldspar-rich layers were more competent than the darker-colored mica-rich layers. Photo is about 25 cm across.

This particular rock is from the Precambrian basement complex of the Death Valley region. Click here to see the Geology of Death Valley National Park through photos.

click here for more photos of ductile deformation.

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