Case-hardening of vertical faces of alluvium and colluvium in, and flanking, the Spring Mountains, Nevada, begins within one or two years after exposure and may proceed to the extent that samples break through clasts. The alluvium and colluvium consist primarily of carbonates, and the cementation which causes the case-hardening appears to be due to solution of the sand-sized and finer carbonate fractions and subsequent deposition of calcite. Above present drainage channels the case-hardening seems to be caused by surface runoff, and the rapidity and degree of cementation is controlled by the texture of layers and lenses within the colluvium and alluvium. Along the present drainage, the case-hardening appears to be due to influent seepage from the streams during spring runoff or during infrequent summer showers and is little affected by texture.

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