May 3, 2008 Willapa Hills-Mima Mounds field trip

On this trip we will examine the effects of the December 2007 flood along the Chehalis River and in the Willapa Hills. The effects include stream channel shifts, flood damage to homes, property and infrastructure; deposits of sediment and debris (including logs), and landslides. We will also examine the local geology and assess what role the geology may have played in the hazards that unfolded. We will also visit the Mima Mounds at the WADNR Mima Mounds Natural Resource Conservation Area as well as the DNR gravel pit along Bourdeaux Road, slight south of the NRCA, where a cross section of a Mima Mount and its underlying gravelly substrate can be observed.

STOP 1: FLOOD DAMAGE ALONG RIVER ROAD.

STOP 2: QUARRY EXPOSURE OF COLUMBIA RIVER BASALT WITH COLUMNAR JOINTING.

STOP 3. EXPOSURE OF PRE-COLUMBIA RIVER BASALT ASTORIA FORMATION SEDIMENTARY ROCKS IN THE CHEHALIS RIVER NEAR DRYAD.

STOP 4. COLUMBIA RIVER BASALT ALONG ELK CREEK ROAD (Drive by no stop).

STOP 5. LANDSLIDE IN LINCOLN CREEK FORMATION SANDSTONES ALONG SR6 WEST OF PE ELL.

STOP 6. FLOOD DAMAGE AND DEPOSITS OF SEDIMENT, LOGS, AND DEBRIS ALONG THE CHEHALIS RIVER AT CERES ROAD BRIDGE.

STOP 7A. LANDSLIDE OF SEDIMENTARY ROCKS AND COLUMBIA RIVER BASALTS ALONG NORTH VALLEY WALL OF CHEHALIS RIVER OFF CERES ROAD.

STOP 7B. DEPOSITS OF GLACIALLY-DERIVED SANDS AT ABOVE SITE.

STOP 8. MIMA MOUNDS NATURAL RESOURCE CONSERVATION AREA.

STOP 9. BOURDEAUX ROAD EXPOSURE OF MIMA MOUND.

Map 1 for Willapa_Mima stops 1 to 7

Map 2 for Willapa_Mima stops 8 and 9

References

Washburn, A. L., 1988, Mima mounds--An evaluation of proposed origins with special reference to the Puget Lowlands: Washington Division of Geology and Earth Resources Report of Investigations 29, 53 p.

 

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