Holocene Arroyo Cut and Fill Cycles, South-Central Washington
Matthew Ian Durkee
Ephemeral streams have cut deeply incised arroyos into alluvial and eolian sediments in many of the watersheds within the Yakima Training Center (YTC) military reservation, south-central Washington. The most recent channel incision episode along Selah Creek is primarily attributed to multiple failures of an irrigation reservoir dam during the winters of 1909 and 1910. The modern arroyo exposed evidence of at least one previous episode of arroyo incision to a depth of ~4 m that occurred just prior to 1530- 1340 cal yr BP. Filling of this paleo-arroyo with fine to coarse grained sand ceased between 650-103 cal yr BP. Changes in paleoclimatic conditions resulting in an increased sediment supply and/or flood magnitude and frequency could have contributed to the initiation of incision of paleo-arroyo(s) within the Selah Creek basin. Almost no overlap of the timing of arroyo incision exists between the northwestern and southwestern U.S. which allows for the possibility of negative correlation between regions.
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