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Fossil sand/mud ripples that somehow survived metamorphosis into quartzite? Or as was suggested when I posted this picture to Facebook, perhaps these are crenulation foliations: "Crenulations form when an early planar fabric is overprinted by a later planar fabric. Crenulations form by recrystallisation of mica minerals during metamorphism. Micaceous minerals form planar surfaces known as foliations perpendicular to the principal stress fields."
H5_MetamorphosedRipples.jpg (425 Kb) (under photos/23/0815-18_WyomingVan/0817_SnowyRangeDayhike/)
By Alan Silverstein, ajs@frii.com (page updated Sun Mar 9 14:33:54 MDT 2025)