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Figure 2
TOP: view upstream of the channel of Pancho Rico Creek and a strath that is adjacent to and approximately 1.5 m above the channel. The tendency for fine grained sedimentary rock to rapidly (as little as 30 days; Montgomery, 2004) disintegrate as a consequence of shrinking and swelling, caused by wetting and drying, is illustrated by the small piles of gray regolith above and below the word “strath” in the photo. Both piles are disintegrated cobbles of Pancho Rico Formation rock, which also constitutes the floodplain/strath. The gray color of the disintegrated cobbles indicate that shrinking and swelling completely disrupted the rock before it was oxidized, which confirms that the process occurred relatively quickly.

BOTTOM: view downstream of the strath terraces at Arroyo Seco, Sierra de Salinas, California Coast Ranges. The straths underlying the highest terraces in the view are approximately 25 m above the Arroyo Seco channel, and no longer affected by erosional processes associated with Arroyo Seco. Note that a strath is presently forming along the meandering channel of the Arroyo Seco.

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Uploaded: Dec22 09

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Antonio Garcia
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