PROCESSES AND TIMING OF HOLOCENE DEPOSITION, CHANNEL INCISION AND COINCIDENT ARCHAEOLOGY, HANSON CREEK, WASHINGTON
Stratigraphic evidence suggests a transition from an aggrading braided system to an expansive, fine grained, alluvial step-pool sequence that continually aggraded throughout the mid- to late- Holocene. A single, 9-m deep incision of a 1.8 km reach occurred around AD 1900. Low gradient, fine grained, organic-rich, sediment suggests prolonged periods of ponding at three locations throughout the incised reach, adjacent to evidence of ground-water springs. The intervening reaches exhibit comparatively high gradients for unconsolidated alluvium.
The chronological and paleoenvironmental data was correlated with the abundant lithic and anthrosol evidence to provide a comprehensive understanding of the relationship between the fluvial environment and the timing, distribution, and preservation of human occupation sites near Hanson Creek throughout the Holocene.The timing and physical environmental conditions associated with the deposition and erosion of Holocene sediment in the Hanson Creek watershed will supplement the minimal data available on arroyo formation in the northwestern U.S. and allow a comparison with previous alluvial chronologies from the region.