Abstract

Fields of correlation points were constructed by graphically correlating phi median grain sizes and sorting coefficients of sediments forming the volcanic siltstones. Comparison of the constructed fields with those of typical loess and ash formations suggests that textures of the siltstones of the middle Oligocene-lower Miocene John Day Formation in eastern Oregon are more characteristic of ash then of loess. Physical resemblance of the siltstones to massive loess deposits is due partly to the continuous homogenizing action of burrowing animals, root-wedging, and frost heaving which destroy what otherwise might be sharp contrasts in texture and in bedding structures within the John Day siltstones.

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