Report of Investigations 35, Digital Landslide Inventory for the Cowlitz

Digital Landslide Inventory for the Cowlitz County Urban Corridor, Washington

by Karl W. Wegmann

WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES Report of Investigations 35 version 1.0 May 2006 DISCLAIMER Neither the State of Washington, nor any agency thereof, nor any of their em- ployees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or other- wise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the State of Washington or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the State of Washington or any agency thereof.

WASHINGTON DEPARTMENT OF NATURAL RESOURCES Doug Sutherland—Commissioner of Public Lands

DIVISION OF GEOLOGY AND EARTH RESOURCES Ron Teissere—State Geologist David K. Norman—Assistant State Geologist

Washington Department of Natural Resources Division of Geology and Earth Resources PO Box 47007 Olympia, WA 98504-7007 Phone: 360-902-1450 Fax: 360-902-1785 E-mail: [email protected] Website: http://www.dnr.wa.gov/geology/

Published in the United States of America

ii iii Contents

Abstract...... 1 Introduction...... 1 Previous landslide studies...... 2 Project history...... 2 Definition of landslide types...... 3 Landslide inventory database...... 6 Data collection methods...... 7 Aerial photograph reconnaissance...... 7 Field verification...... 7 Compilation of GIS inventory and database...... 10 Results...... 11 Discussion...... 12 Geologic controls...... 12 Landslide types...... 17 Possible triggering mechanisms...... 18 Inventory limitations...... 19 Potential uses...... 19 Planning...... 19 Hazard map calibration...... 20 Regional analyses...... 20 Summary...... 20 Acknowledgments...... 20 References cited...... 21

Appendix Bibliography of slope-stability investigations within the Cowlitz County urban corridor...... 23

Figures Figure 1. Map showing location of the Cowlitz County urban corridor landslide inventory area...... 2 Figure 2. Graph showing the 73-year precipitation record for Longview, Washington...... 2 Figure 3. Map of the inventory area showing the distribution of identified deep-seated and shallow landslides and potentially unstable slopes...... 3 Figure 4. Map and photographs of the Aldercrest–Banyon landslide, Kelso...... 4 Figure 5. Illustrations showing landslide classification, the anatomy of an idealized complex earth slide–earth flow, and landslide elevations and dimensions used in the inventory database...... 5 Figure 6. Map and photographs of a large deep-seated landslide along the south side of the Kalama River, illustrating recent shallow-landslide activity within slide body and off slide scarp...... 6 Figure 7. Illustration of morphological changes to an idealized landslide through time, and corresponding activity-state descriptions used in this study...... 7 Figure 8. Illustration of slope gradients used in the inventory database...... 10 Figure 9. Generalized stratigraphic correlation diagram for the study area...... 11 ii iii Figure 10. Graph of the relationship between the percent of total landslide area originating from a given geologic unit and the percent of the total study area underlain by that geologic unit ...... 11 Figure 11. Photographs of deeply weathered (saprolitic) volcaniclastic sandstone and conglomerate of the Goble Formation exposed in a roadcut along Bodine Road.....12 Figure 12. Photographs of deeply weathered (saprolitic) volcanic tuff of the Goble Formation exposed in roadcut along Bella Vista Road...... 12 Figure 13. Photographs of cross-bedded and lenticular sandstone of the Sandy River Mudstone...... 13 Figure 14. Photographs of a large deep-seated rock slide along the north side of the Kalama River illustrating a large-scale bedrock landslide...... 13 Figure 15. Photograph of the contorted foundation of a house destroyed by a landslide developed within deeply weathered volcaniclastic rocks of the Goble Formation...... 14 Figure 16. Photographs of a small rotational deep-seated landslide in weathered sediments of the Cowlitz Formation along Columbia Heights Road...... 14 Figure 17. Map and photographs of the dormant Beigle Mountain landslide complex, located northeast of Toutle...... 14 Figure 18. Map and photographs of the dormant–relict deep-seated rotational to translational Columbia Heights landslide...... 15 Figure 19. Geologic cross section and photographs illustrating geologic controls on the Aldercrest–Banyon landslide...... 16 Figure 20. Photographs of the Kelso “K” small deep-seated earth slide–flow, which initiated in fluvial silts and clays of the Troutdale Formation...... 16 Figure 21. Photograph of a small deep-seated translational earth slide–flow north of Woodland, which initiated in fine-grained Pleistocene Missoula flood deposits...... 17 Figure 22. Photographs of a small recent rock fall within a larger dormant–young rock fall–slide located above State Route 4, approximately 0.5 mi east of Stella.....17 Figure 23. Map showing the distribution of active landslides superimposed on the Davis Terrace landslide complex...... 17 Figure 24. Photograph of a human-induced, small deep-seated rotational earth slide–earth flow north of Kalama along Spencer Creek Road...... 18

Table Table 1. Database attribute descriptions for the 82 fields found in the ESRI shapefiles ccuc_deep_seated_landslides.shp and ccuc_shallow_landslides.shp...... 8

iv Digital Landslide Inventory for the Cowlitz County Urban Corridor, Washington

by Karl W. Wegmann Washington Division of Geology and Earth Resources PO Box 47007; Olympia, WA 98504-7007

Abstract This report contains a digital geographic information systems (GIS)–based inventory and database for identified deep-seated and shallow landslides within the Cowlitz County urban corridor, Washington, extending from slightly north of the Toutle River south to the Cowlitz County–Clark County boundary, and encompassing primarily non-commercial timber lands on either side of Interstate Highway 5. The inventory contains specific information about each landslide, such as: landslide type; slide dimensions; certainty that the mapped feature is a landslide; inferred state of activity derived from geomorphologic and engineering data; whether the slide was previously identified in geotechnical, landslide inventory, or geologic mapping reports; geologic unit(s) involved; and affected infrastructure. The GIS files composing the inventory are publicly available, and are intended to be of use for a variety of state, county, and city land-use planning and development purposes. This inventory should be considered an initial baseline for future site-specific landslide-related studies within the Cowlitz County urban corridor. It is not intended to be detailed enough to replace site-specific investigations by qualified (licensed) experts. In response to the costly Aldercrest–Banyon landslide of 1998 and other recent damaging landslides in Cowlitz County, the Washington Division of Geology and Earth Resources began its GIS-based landslide inventory and slope stability mapping project for the Cowlitz County urban corridor in 2000. In total, 825 landslides (593 deep-seated and 232 shallow) were identified within the 260 mi2 project area. Eighty percent of the inventoried landslides were not previously identified in available geologic mapping, landslide inventories, and geotechnical reports. Of the landslides identified on aerial photographs, 70 percent were field checked, and of these, 20 percent exhibited evidence of movement within the past 10 years. Deep-seated slides range in size from 0.03 to 410 acres, covering a combined total of 11,362 acres of terrain, and occur on slopes with gradients as low as 10 percent (6°). Shallow landslides cover a combined total of 62 acres and range in size from 0.005 to 2.5 acres. The study area is characterized by moderate to steep slopes that tend to move via slow to moderate, rotational to translational rock or earth slides. In general, the study area is underlain by high-plasticity clay-rich soils and deeply weathered Tertiary bedrock. Slides occur within all rock units regardless of age, but have the highest rate of occurrence on steep to moderate slopes underlain by deeply weathered volcanic tuffs and volcaniclastic sedimentary rocks of the Goble, Cowlitz, Toutle, and Troutdale Formations and the Sandy River Mudstone, all of Tertiary age. The majority of slides appear to have moved in response to natural causes, such as above-average annual or multi-annual precipitation and antecedent soil moisture conditions. Some of the now-dormant deep-seated slides may have been seismically triggered, and others may have moved in response to rapid drawdown of late Pleistocene glacial outburst floodwaters along the Columbia River and its tributaries. Human actions, such as the alteration of slope morphology and hydrology by development, forestry, and surface mining operations, and improper placement and design of fill material on slopes, have contributed to the initiation of new and reactivation of dormant deep-seated slides.

Introduction As attested to by recent landslide disasters in California, the ordinance, which it adopted in 1996 (Cowlitz Co. Ordinance tsunami tragedies around the Indian Ocean, and earthquake- 96-104). Section 19.15.150 of this ordinance addresses geologic induced liquefaction during the 2001 Nisqually earthquake hazard areas, including landslide hazard areas. Identification of (Walsh and others, 2002), the need for mapping potential geologic landslide areas within the rapidly urbanizing areas of the county hazards such as landslides, tsunami inundation zones, and areas is an important first step toward effective implementation of the susceptible to earthquake-induced liquefaction is increasing in geologic hazard section of this ordinance. step with regional population growth and expansion of the urban The purpose of this landslide mapping project is to update fringe into once sparsely populated rural forest and agricultural and expand a previous slope stability study for the Longview– lands. Nationwide, landslides account for approximately $1.5 Kelso urban area (Fiksdal, 1973), and to extend slope-stability billion in economic losses—more than all other natural disasters mapping to include the high-growth areas in the Interstate combined—and 25 to 50 deaths annually (Schuster, 1996). Highway 5 (I-5) corridor from the Clark County line in the south Western Washington, with its geologic conditions, high annual to the Toutle River in the north (Fig. 1). This report presents an precipitation, and areas of considerable topographic relief, is one expandable geographic information system (GIS) inventory of of the more landslide-prone areas of the country. remotely sensed and field-verified landslides within the Cowlitz With passage of Washington’s Growth Management Act and County urban corridor. The products of this study consist of (1) amendments in 1990 and 1991, counties and cities were directed a GIS inventory of identified landslides within the study area to delineate critical areas (including those subject to geologic and presented as ESRI shapefiles, (2) associated metadata, (3) digital hydrologic hazards) to aid in formulating regulations governing photographs of individual landslides and associated text, (4) development in such areas (Brunengo, 1994). Although Cowlitz 1:24,000-scale landslide inventory maps for each 7.5-minute County did not meet the Growth Management Act’s population quadrangle in the inventory area, presented as PDF files, and (5) threshold and was not required to develop a comprehensive plan, this explanatory text. the county was required to establish a critical-areas protection iv REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON

This is the second of three eventual products of the declaration for 138 homes affected by the landslide (Burns, Washington Division of Geology and Earth Resources (DGER) 1999). Damage to private and public property for this landslide landslide inventory and slope-stability mapping project for the alone is estimated to be more than 30 million dollars (Buss and Cowlitz County urban corridor. The first report (Wegmann, others, 2000). 2003), which covered the south half of the project area, is entirely In response to the Aldercrest–Banyon disaster and numerous superseded by this one. The third data product will be a relative other recent landslides, Cowlitz County officials, DGER slope-stability map for the study area, delineating areas in which geologists, and state legislators representing southwestern the combination of geologic and topographic factors indicate an Washington recognized the need for improved slope-stability increased likelihood of future slope instability, based upon this mapping within the urbanizing I-5 corridor. During the second digital landslide inventory and compiled geologic mapping. half of 1998, in preparation for the 1999–2001 biennial state

Previous landslide studies LEWIS CO. The only previous landslide assessment projects of significant COWLITZ CO. River scope in the Cowlitz County urban corridor were an inventory River Fork and slope-stability map by Fiksdal (1973) and an inventory by Toutle N 504 Wegmann (2003). Their data are incorporated in this report. CASTLEROCK SILVERLAKE TOUTLE Additional geologic mapping by Roberts (1958), Livingston ABERNATHYMOUNTAIN Silver Lake S Castle Rock Fork (1966), Myers (1970), Phillips (1987a,b), Evarts (2001, 2002, CO. WAHKIAKUM 2004), Kleibacker (2001), and McCutcheon (2004) identified landslides at varying levels of detail and map scale. Private Cowlitz 5 geotechnical consulting reports also provide information on OAK COAL River MOUNT POINT CREEK KELSO Columbia Kelso BRYNION potentially unstable slopes, landslide distribution, and the state C 4 oweeman of landslide activity within the study area (see Appendix). The OREGON Longview private geotechnical reports consulted during the compilation of River this report were obtained from Cowlitz County and the cities of Kelso, Kalama, and Woodland. These reports were used along River KALAMA RAINIER CREEK WOOLFORD with the above-mentioned landslide and geologic-mapping Kalama Kalama reports to aid the compilation of this inventory. The geographic 46°N distribution of individual private geotechnical reports is available 0 5 10 mi 123°W in the shapefileccuc_report_boundary.shp . 503

0 5 10 15 km DEER R. ARIEL ISLAND Lewis Project history Woodland WOODLANDCLARK CO. EXPLANATION Infrastructure damage from landslide activity has been a Cowlitz County urban corridor recognized problem for southwestern Washington, including the landslide inventory area (approximate) greater Longview–Kelso urban area, for many years (Shannon & Aldercrest–Banyon landslide Wilson, 1965; Thorsen, 1989; Harp and others, 1998). Periodic KELSO U.S. Geological Survey increases in the activity of landslides in southwest Washington map area generally coincide with increases in the amount and duration 7.5-minute quadrangle name of regional precipitation. Significantly higher than normal Figure 1. Location of the Cowlitz County urban corridor landslide in- precipitation was recorded for most of western Washington, ventory area. including Cowlitz County and the Longview–Kelso urban area, beginning in the 1995 water year (October 1994 to 70 September 1995) and lasting through the 2000 water year (Fig. six-year period of 73-year average = 45.9 in. above-normal precipitation 2). Furthermore, the 1996 and 1997 water years, as recorded in 60 Longview, were the wettest two years on record for the past 73 years (Western Regional Climate Center, 2005). This multi-year 50 increase in precipitation resulted in elevated ground-water levels 40

that, in turn, reactivated many dormant deep-seated landslides Precipitation (in.) throughout southwestern Washington (Burns and others, 1999). 30 Specifically, in February 1998, a deep-seated earth slide–earth flow reactivated in the Aldercrest neighborhood of Kelso 20 1930 1940 1950 1960 1970 1980 1990 2000 (Aldercrest–Banyon landslide; Figs. 1, 3, 4; see also Fig. 19); Water Year in October of 1998, President Clinton issued a federal disaster Figure 2. Seventy-three-year precipitation record for Longview, Wash- ington (Western Regional Climate Center, 2005). A ‘water year’ runs from October of the previous year through September of the current year. Note 1. Note that each private geotechnical investigation was conducted for a that the six-year increase in precipitation at the end of the 1990s cor- specific purpose during a distinct period of time, and subsequent use of a relates to a period of increased landslide activity and damage along the preexisting geotechnical report may not be appropriate. Cowlitz County urban corridor. REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON

budget, the Washington State Department of Natural Resources usually moves over a relatively confined zone or surface of shear (DNR) requested and received funding from the legislature (Jackson, 1997), but the general term ‘landslide’ can also include for geologic-hazard mapping to evaluate ground stability in falls, topples, spreads, and flows (Cruden and Varnes, 1996). The high-growth areas, and to provide geologic expertise to small downslope movement of geologic materials may be triggered communities. DGER began the Cowlitz County Urban Corridor by a number of natural factors including intense rainfall, long- Landslide Hazard Mapping Project in February of 2000. An area duration precipitation, rapid snowmelt, surface- and ground- of approximately 250 mi2 was identified by Cowlitz County water level changes, wave or stream erosion, earthquake shaking, GIS Department staff as critical to the urban-growth needs of and volcanic eruptions (Wieczorek, 1996). Human actions such the county and in need of improved slope-stability mapping. as the rerouting or concentration of water on a slope, improper Partnerships were established with geologists from Oregon State placement of fill material on the head of a slope, and cutting University and the U.S. Geological Survey (USGS) to coordinate into the toe of a slope can all increase the likelihood of future various mapping projects in order to provide geologic coverage landslide activity. for the entire study area at a scale of 1:24,000. In 2003, DGER For the purposes of this study, landslides are divided into published a landslide inventory for the southern half of the study two kinds, based mainly on size: deep-seated and shallow. area (Wegmann, 2003) in order to provide available data in a Deep-seated landslides are defined as slides with primary timely manner to local governments, geotechnical consultants, planes of failure well below the rooting depth of the vegetation and local property owners. This report incorporates the previously and generally into the bedrock or regolith below the soil or published data as well as new inventory data for the areas north colluvial layer (Gerstel, 1999). Varnes (1978) and Cruden and and west of Kelso (Wegmann, 2004) (Figs. 1, 3). Varnes (1996) classified deep-seated landslides based upon their mechanism of movement into falls, topples, slides, and flows Definition of landslide types (Fig. 5a). They can be large in areal extent and once activated or reactivated, by either natural causes or land-management ‘Mass wasting’ and ‘landsliding’ are general terms covering a wide practices, often prove to be expensive and difficult (sometimes variety of mass-movement landforms and processes involving impossible) to mitigate. Locations of deep-seated landslides are the downslope transport, under gravitational influence, of soil difficult to predict through modeling, and as a result, identification and rock material en masse. In sliding, the displaced material of existing landslides serves as one of the best indicators of the potential for future landslides (Gerstel, 1999). Shallow landslides are defined as slides that initiate within the soil and (or) colluvial mantle, and generally are smaller

SR 504 in areal extent than deep-seated landslides (Gerstel, 1999). Toutle Toutle R. Shallow landslides include the following types: debris or earth slides, flows, topples, falls, and spreads (Cruden and Varnes, Silver Lake Castle 1996). Shallow landslides are commonly caused by the buildup Allen Bros. Drive Rock Beigle Mountain of pore-water pressures in the soil mantle during periods of

SR 411 heavy precipitation and (or) rapid snowmelt (Wieczorek, 1996). Shallow landslides occurring on steep slopes at the heads of

Columbia zero-order basins or colluvial hollows can change into debris Heights flows downslope. Areas containing many shallow landslides may Aldercrest–Banyon Columbia Heights indicate potentially unstable slopes that are sensitive to land-use modifications (such as road building, timber harvest, or surface Longview

Cowlitz R. Cowlitz mining operations). Alpha Drive Kelso Shallow landslides are commonly observed in association Coweeman R. with underlying deep-seated landslides, such as on scarps (Fig. Davis Terrace 6), on the toe, where rotated blocks have resulted in over-

Kalama River steepening of segments of the slope, where drainages have been EXPLANATION disrupted and redirected, or where material strengths have been identified landslide area Kalama R. Fallert Bridge reduced by mechanical (shearing) and chemical weathering potentially unstable area processes (Gerstel, 1999). Areas of steep topography may be SR 504 landslide name at higher risk for shallow landsliding, whereas deep-seated landslides are not confined to a particular slope angle, occurring on slopes as low as 6 degrees in the study area. In general, areas underlain by strong rocks maintain steeper slopes that are more prone to shallow landslide activity, whereas areas underlain by Woodland Lewis R. weak rock maintain gentler slopes and are more prone to deep- seated landslides. Figure 3. Shaded-relief map of the Cowlitz County urban corridor land- Although shallow landslides are included in the database slide inventory area showing the distribution of 825 identified deep-seated and shallow landslides, and potentially unstable slopes where landslides and were mapped where identified from aerial photographs or in were either not identified or too small to map individually. Named land- the field, the main emphasis of this inventory is on deep-seated slides are discussed in the text. SR, State Route. landslides. REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON

Coweeman R. 0 400 ft

scale

Grim Rd.

Banyon Dr.

Aldercrest Dr.

cross section GRABEN (Fig. 19a)

pre-existing dormant scarp reactivated Aldercrest–Banyon slide

B 273 C 264 scarp

back-tilted trees

315 sag pond destroyed houses 267 264 271

272 311 D 271

270 back-rotated block 262 258 203 202 0 1000 ft scale 259 REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON

ROCKFALL TOPPLE BLOCK SLIDE

ROCK or EARTH SLIDE ROCK or EARTH SLIDE EARTH FLOW DEBRIS AVALANCHE / FLOW

crown B ORIGINAL GROUND cracks CROWN SURFACE crown elevation MAIN SCARP

head elevation EARTH SLIDE HEAD transverse TOP MINOR SCARP toe elevation cracks WEDGE FAILURE transverse RIGHT FLANK (LATERAL SCARP) cracks TOTAL RELIEF EARTHtransverse FLOW longitudinal ridges fault zone E radial R DISPLACED MATERIAL U cracks PT U MAIN BODY R OF CE FOOT SURFA SLIDE TIP TOE SURFACE OF WIDTH SEPARATION toe of surface of TOTAL rupture LENGTH

Figure 5. A. Landslide classification (modified from Varnes, 1978, and Cruden and Varnes, 1996). B. Anatomy of an idealized complex earth slide–earth flow (modified from Varnes, 1978, and Cruden and Varnes, 1996). Labeled components apply to most landslides. Landslide elevations and dimensions used in the inventory database are shown as colored arrows and points; see inventory database fields CROWN_ELEV, HEAD_ELEVA, TOE_ELEVAT, TOTAL_RELI, TOTAL_LENG, and SLIDE_WIDT (Table 1).

Figure 4. (previous page) Aldercrest–Banyon landslide, Kelso (see Fig. 1 for location). Landslide motion began on this deep-seated earth slide-earth flow in February 1998, and by October of the same year, had affected 138 homes. The landslide is about 3000 ft wide by 1500 ft in length, and the main scarp is over 100 ft high in places. A. Stereo pair of the landslide from 1999 DNR aerial photographs. For a three-dimensional view, print the photo pair, focus your eyes on the far distance, and bring the photo pair up in front of your face at your normal reading distance; or, use a pocket stereoscope. The slide is interior to a larger landslide feature, as defined by the pre-existing dormant scarp. The straight line is the approximate location of the geologic cross section shown in Figure 19a. B. Inventory map of the landslide area. Active landslides are shown in yellow, dormant landslides in red, and slides not field-checked in blue; active landslides moving within the boundaries of larger dormant landslides appear orange. The three-digit numbers are unique identification numbers for each landslide polygon [see database field GIS_ID]. The black arrows indicate approximate landslide movement directions. Landslide scarps are shown as hachured lines, the colors of which correspond to the color of the associated landslide polygon. The map shows where part of a dormant landslide (GIS_ID 271) was reactivated in 1998, resulting in the Aldercrest-Banyon landslide (GIS_ID 272). The slight apparent difference in mapped landslide and scarp size and location between this map and the stereo pair in A is due to distortion created by the use of unrectified aerial photographs. The true size and location of the reactivated Aldercrest-Banyon landslide is shown in this inventory map. C. View northwest along the main scarp of the landslide, August 2000. Note the destroyed houses and tilted trees at the base of the scarp. Prior to the landslide, these houses were slightly above the elevation of the top of the scarp. This photo was taken in the former basement (light gray area on the left) of a house now at the bottom of the hill outside the photo area. The scarp exposes fluvial gravels and sands of the Troutdale Formation. D. View to the southeast across the middle section of the landslide, June 2000. The houses in this view are uninhabitable. Note the internal rotation within the landslide body as evidenced by the back tilting of the distant house. REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON

Landslide inventory database direction of landslide movement from both geologic and aerial photographic interpretations (ccuc_landslide_directions.shp), This landslide inventory contains information on 825 landslides, and identified springs associated with landslides (ccuc_spring_ 593 of which are classified as deep-seated, and is presented as locations.shp). Complete descriptive information pertaining to eleven ESRI shapefile themes .shp( ) and associated database files the inventory files may be obtained from the project metadata (.dbf). The shapefiles may be used individually or together to files, arranged one per shapefile. create custom maps tailored to users’ needs. Polygon themes are For each landslide, up to 82 characteristics (Table 1) were used for deep-seated landslides (ccuc_deep_seated_landslides. recorded and compiled in the .dbf files associated with the shp), shallow landslides (ccuc_shallow_landslides.shp), the shapefilesccuc_deep_seated_landslides.shp and ccuc_shallow_ geographic extent of the study area (ccuc_study_area.shp), landslides.shp. The inventory database is intended to allow for slopes considered to be potentially unstable due to geologic specialized queries of landslide parameters for the purposes conditions but not mapped as individual landslides (ccuc_ of specific projects; for example, it is possible to query for potentially_unstable_slopes.shp), the approximate boundaries all active landslides in sediments of the Troutdale Formation, of areas covered by private geotechnical and other governmental greater than 0.5 acre in size, and lying within the boundaries reports consulted during the construction of this inventory (ccuc_ of the Kalama 7.5-minute quadrangle (nine landslides identified report_boundary.shp), and sag ponds or closed depressions found in such a query). The database (.dbf) files associated with each within landslide boundaries (ccuc_sag_ponds.shp). A line theme shapefile can be opened and manipulated either within ESRI’s delineates the main and internal scarps of deep-seated landslides GIS software, or with spreadsheet or database software such as (ccuc_deep_seated_landslide_scarps.shp). Point themes are Microsoft Excel or Access or Systat Software Inc.’s SigmaPlot. used to indicate the centroid, or approximate center, of each landslide polygon (ccuc_deep_seated_landslide_locations. shp and ccuc_shallow_landslide_locations.shp), the inferred

A shallow slides on main scarp

main scarp

slide

Kalama River

B slide body C × main scarp shallow slide shown in B main shown in C scarp

Figure 6. Large (65-acre) deep-seated rotational to translational rock slide along the south side of the Kalama River (GIS_ID 20) (NE¼ sec. 3, T6N R1W), illustrating shallow landslide activity within the slide body and on the main scarp. It is believed that this landslide initiated in volcanic flows and volcaniclastic sediments of the Goble Formation. A. Map of recent (post-1996) shallow landslides (in orange) developed within the deep-seated slide body (large red polygon) and on the main scarp. Many of the large bedrock-dominated landslides in the study area have recent shallow slides on their scarps or within the slide body itself. B. View to the southeast from the western margin of the main scarp. The main scarp in the foreground is basaltic andesite, with well-developed joints that dip steeply in the direction of landslide movement (strike N89°E, dip 59°NW). Bedrock discontinuities such as joint sets may in part control the location of bedrock landslides in the study area. C. View to the south from the head of the landslide to the main slide scarp, which is above the distinct slope break in the middle of the photo. A recent (post-1996) shallow colluvial landslide scar is visible on the main scarp. This shallow landslide began within the thin soil mantle developed on top of the bedrock scarp. REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON

Data collection methods and mapped on clear plastic (acetate) overlays. A unique identification number was assigned to each feature. The development of this landslide inventory was completed in three phases: (1) initial landslide identification through aerial- Field Verification photograph reconnaissance mapping; (2) field verification of landslide areas; and (3) creation of ESRI shapefiles containing Field verification of suspected landslides identified during the landslide polygons and associated attributes and related data initial aerial photograph analysis, as well as mapping of geologic files. Previous landslide inventories in Washington, Oregon, conditions related to slope instability, began in the spring of and northern California have shown that the combination of 2000 and continued through the fall of 2002. Field verification aerial-photograph interpretation and field verification is an of suspected landslides was conducted by walking the identified effective method for properly identifying deep-seated landslides target area whenever access, topography, and time would allow. (Washington Forest Practices Board, 2001; Dragovich and Where necessary, landslide boundaries were adjusted on the Brunengo, 1995; Gerstel, 1999; Robison and others, 1999; Wills aerial photograph overlays as dictated by field evidence. Features and McCrink, 2002). suspected of being landslides from the original aerial-photograph inventory, but that lacked field evidence, were not included in Aerial Photograph Reconnaissance the final inventory. For each field-verified landslide, Inoted the degree of development of landscape features commonly During the winter and spring of 2000, potential deep-seated associated with deep-seated landslides (Fig. 5b), such as a main landslides and visible recent shallow landslides were delineated scarp, minor internal scarp(s), lateral scarps, hummocky ground, using DNR aerial photographs from 1993 (scale 1:12,000, black tension cracks, exposed soil and (or) rock, disturbed stream and white; project SW93) and 1999 (1:12,000, color; SW-C- patterns, closed depressions or sag ponds, springs, and disturbed 99) and to a lesser extent 1996 and 1974 (1:12,000, black and trees. The number of these features and their degree of erosion white; SWH-96, SW-74) and 1978 (1:24,000, color; SW-C- or degradation served as a qualitative measure of the certainty of 78), and USGS aerial photographs from 1951 (1:48,000, black identification, assigned as ‘definite’, ‘probable’, or ‘questionable’ and white; GS-QP) [see database fields AP_1 to AP_4 (Table [see database fieldsCERTAINTY and C_A (Table 1)]. 1)]. The 1993 and 1996 photo sets provided full coverage for The field-assigned activity state of identified landslides was the study area while the 1999 and 1951 photo sets provided based upon available geomorphic indicators, as mentioned above, approximately 90 percent coverage. Aerial photograph pairs and includes four possibilities: active; dormant–young; dormant– covering the entire study area were systematically viewed using mature; and dormant–relict [see database fields ACTIVITY and a mirrored stereoscope. Suspected landslides, containing distinct C_A (Table 1)]. The degree of erosion of the landforms associated geomorphic features such as head scarps, benched topography, with landslides can be used as an indictor of the activity state of distinct lateral margins, and displaced drainages, were identified the landslide (Fig. 7), which in turn can be used as a guide for

A Dy Dm Dr

Activity state Code Main scarp Lateral scarp Body Active, reactivated A Sharp Sharp Undrained depressions; hummocky with angular blocks separated by scarps; may be chaotic Dormant–young Dy Distinct but not Distinct but not sharp; shallow Undrained and drained depressions; hummocky with sharp; shallow failures; lateral streams are fed by blocks separated by less-distinct scarps; may still be cha- and (or) regressive small tributaries off body; streams otic; scarps (toes of upper blocks) often oversteepened failures incised with side slope slumping (convex in contour and profile) with shallow failures; defined draws developing on edges of internal blocks Dormant–mature Dm Subdued but Subdued but apparent; lateral Drained but atypical stream pattern; depressions no lon- apparent streams fed by tributaries extend- ger apparent; distinctly rolling or benched topography ing well into the slide body Dormant–relict Dr Vague to very Vague or very subdued such that Normal (typical) drainage pattern; smooth to undulating subdued and dis- lateral boundaries are difficult to topography sected identify

Figure 7. Morphological changes to an idealized landslide through time, and corresponding activity-state descriptions used as a qualitative means to assess the potential age and state of activity of landslides (modified from Turner and Schuster, 1996). The code associated with each activity state is the value used in the ACTIVITY field in the database (see Table 1). The diagrams depicting the morphologic change of an idealized landslide through time (modified from McCalpin, 1984) are for an arid or semiarid climate. In western Washington, the humid-temperate climate commonly results in rapid revegetation of the landslide body, commonly making it difficult to identify distinct landslide features. REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON - e S h er

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Description Washington State Plane x-coordinate at approximate center of landslide, State Plane South (FIPS Zone 4602) Washington State Plane y-coordinate at approximate center of landslide, State Plane South (FIPS Zone 4602) First aerial photo used to identify the landslide area Second aerial photo used to identify the landslide area Third aerial photo used to identify the landslide area Fourth aerial photo used to identify the landslide area Name of primary 1:24,000-scale U.S. Geological Survey (USGS) topograp ic Name of secondary 1:24,000-scale USGS topographic sheet that contains th landslide at a scale larger Viewing Scale at which landslide polygon was digitized. than this may give a false level of accuracy Elevation of landslide crown, in feet above sea level, determined from USG 10-meter digital elevation model (DEM) Elevation of landslide head, in feet above sea level, determined from 10- meter DEM Elevation of landslide toe, in feet above sea level, determined from 10-met DEM relief of landslide, in feet, determined by subtracting Total from Direction of movement, which is a visual average the direction slope faces and the direction of movement slide ArcView Length of landslide from crown to toe, in feet, determined of landslide mass (landslide body), in feet, measured on screen across Width widest portion of landslide body ArcView Area of landslide polygon, in square feet, determined ArcView Area of landslide polygon, in square kilometers, determined ArcView Area of landslide polygon, in acres, determined gradient of landslide over its length, in degrees, measured the Average field using a handheld optical reading clinometer gradient for landslide scarp region, in degrees, measured the field Average using gradient for landslide head region, in degrees, measured the field Average using gradient for landslide body region, in degrees, measured the field Average using Attribute Label SPS_X SPS_Y AP_1 AP_2 AP_3 AP_4 QUAD_1 QUAD_2 DIGITIZATI CROWN_ELEV HEAD_ELEVA TOE_ELEVAT TOTAL_RELI MOVEMENT_D TOTAL_LENG SLIDE_WIDT AREA_FT AREA_KM ACRES SI_FIELD SS_FIELD SHS_FIELD SBS_FIELD

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Description Sequential Coordinates defining the features Sequential order Number assigned to landslide during field identification Landslide type identifier: 1, deep-seated active; 2, inactive; 3, deep-seated non–field checked; 4, shallow (both checked and checked) Probability that feature is a landslide: D, definite (field certainty 5 [see field 2 probable (field certainty 4 or 3); Q, questionable C_A]); P, or 1). Note: landslides of rating A, active (field activity 5 [see field Perceived level of landslide activity: C_A dormant–relict (field activity 2 or 1) mature (field activity 3); Dr, Field-determined certainty / activity ranking: 5 (definite active); 4 (prob able / dormant–young); 3 (probable dormant–mature); 2 or 1 (questionabl / dormant–relict) Whether or not landslide was identified in the field (YES) only from aer photos Certainty of landslide boundary location: C, certain (generally shown with A, approximate (generally shown with dashed line) solid line on a map); Primary Second Third Fourth Primary base Primary ian) Second base Second ian) Longitude at approximate center of landslide, in decimal degrees east th prime meridian (negative number denotes of degrees west the prime Latitude at approximate center of landslide, in decimal degrees north the equator Database attribute descriptions for the 82 database fields found in the ESRI shapefiles ccuc_deep_seated_landslides.shp and ccuc_shallow_landslides.shp. The ‘attribute is label’ the name

Attribute Label FID SHAPE GIS_ID FIELD_ID TYPE_CODE CERTAINTY ACTIVITY C_A FIELD_VERI LINE_TYPE SEC_1 SEC_2 SEC_3 SEC_4 TOWN_1 RANGE_1 TOWN_2 RANGE_2 LONGITUDE LATITUDE Table 1. Table of each database field as found in the shapefiles. More information on attribute fields is contained within project metadata. REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON -

on on on on ) - - - - FIELD_ID of the landslide, followed by date photo was taken and FIELD_ID Description or city road (YES NO) Identifies whether slide impacts state, county, Identifies whether slide impacts a house or other building (YES NO) Identifies whether slide initiates in or impacts building foundation fill (YES or NO) Identifies whether slide impacts a natural gas or liquid petroleum pipeline (YES or NO) Identifies whether slide impacts a bridge (YES or NO) State Department of Natural Resources Washington Name designated by the are generally WAUs (DNR) for the watershed administrative unit (WAU). between 10,000 to 50,000 acres in size and are discrete hydrologic units Name designated by DNR for the watershed basin containing individual and smaller than WAUs in size than landslide polygon. Basins are larger WRIAs WRIAs are Area (WRIA). Resource Inventory Water DNR-determined multi-basin in size Filename consists of Filename of digital photo landslide taken by author. the a unique sequential number assigned by the digital camera. For example, file 601_082102_2973.JPG is a photo of landslide number 601 ( August 21, 2002 and recorded by the camera as 2,973rd photo taken on The photo itself and its description are available as part of a seperate taken. data repository item Description of digital photo referenced in DP_1 See de Filename of additional digital photo landslide taken by author. scription of field DP_1 for file naming convention and additional informati Description of digital photo referenced in DP_2 See de Filename of additional digital photo landslide taken by author. scription of field DP_1 for file naming convention and additional informati Description of digital photo referenced in DP_3 See de Filename of additional digital photo landslide taken by author. scription of field DP_1 for file naming convention and additional informati Description of digital photo referenced in DP_4 See de Filename of additional digital photo landslide taken by author. scription of field DP_1 for file naming convention and additional informati Description of digital photo referenced in DP_5 Reference to governmental and (or) geotechnical reports containing informa null value indicates that no geotechnical reports were A tion on landslide. obtained for a given landslide (although they may exist) Additional comments about a given landslide Attribute Label ROAD HOUSE FOUNDATION PIPELINE BRIDGE WAU BASIN WRIA DP_1 DP_1_DESCR DP_2 DP_2_DESCR DP_3 DP_3_DESCR DP_4 DP_4_DESCR DP_5 DP_5_DESCR DATA_SOURC COMMENTS - r - , e S de m d or - - Description gradient for landslide toe region, in degrees, measured the field Average using a handheld optical reading clinometer Approximate average range of gradient values for slope upon which land using a slope grid ArcView slide is developed, in degrees, determined derived from 10-meter DEMs Predominant type of movement exhibited by the slide mass (fall/topple, slide–rota slide–translational, slide–rotational, slide–translational/flow, flow, Varnes spread, other), following the nomenclature of Cruden and tional/flow, (1996) Predominant type of landslide material (rock, earth, debris), following the (1996) Varnes nomenclature of Cruden and Washington The same symbology used for Abbreviated rock type symbol. Division of Geology and Earth Resources 1:100,000-scale geologic maps Structural geologic information obtained either in the field or compiled fro available geologic maps Descriptions of the failed soil/rock unit based upon field mapping by author as well mapping by Evarts (2001, 2002, 2004); Phillips (1987a,b); Liv ingston 1966; Roberts (1958); Kleibacker (2001); McCutcheon (2004) Identifies whether landslide contains a distinct scarp (YES or NO) (YES or NO) Identifies whether landslide has a distinct flank / margin Identifies whether hummocky ground was identified on landslide mass (YE or NO) Identifies whether ground cracking was observed within confines of landsli (YES or NO) Identifies whether internal scarps were observed within confines of landslid (YES or NO) Identifies whether exposed soil and (or) rock were identified on landslide A positive may scarp slope or within confines of landslide (YES NO). indicate recent activity re landslide (recently internal landslides to larger Identifies whether smaller, inactive slide mass) were identified (YES or NO) activated portions of larger deep-seated of main scarp larger Identifies whether shallow landslides off landslide were identified (YES or NO) of slide were Identifies whether incised or displaced streams along margin identified in aerial photo reconnaissance (YES or NO) Identifies whether sag pond(s) within landslide mass were identified (YES o NO) (YES or NO) identified mass were landslide springs within whether Identifies Identifies whether disturbed/distorted conifer trees (believed to be disturbe by landslide movement) were observed within confines of (YES NO) (continued) Attribute Label STS_FIELD RS_GIS MOVEMENT MATERIAL ROCK_TYPE BEDROCK_ST GEOLOGY SCARP FLANK_MARG HUMMOCKY GROUND_CRA INT_SCARPS EXPOSSED_S INT_SLIDE SHALLOW_LA DISRUPTED_ SAG_POND SPRING TREES Table 1 . Table 10 REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON 11 the likelihood of, or potential for, reactivation and movement ft. The database field DIGITIZATI (Table 1) provides the specific of a given landslide. Active or recently active landslides are scale at which each individual landslide and landslide scarp was more likely to continue to move or be reactivated than dormant digitized. All attempts were made to minimize spatial errors landslides. It is important to note that disturbed ground (such as during this step in the project; however, I can not guarantee exact active landslides) in western Washington is revegetated quickly, correspondence between the spatial locations of the digitized and other indicators of active slide movement may or may not features in the GIS inventory and those of features identified on be present and visible in the field; therefore the activity rating aerial photographs and in the field. should be considered approximate, as it is based on cursory field A 10 m digital elevation model (DEM) covering the observations. entire study area was used to determine the crown, head, and Landslides that were found to disturb infrastructure and toe elevations and total relief of each landslide (Fig. 5b) [see buildings (engineered structures), such as homes, roads, bridges, database fields CROWN_ELEV, HEAD_ELEVA, TOE_ELEVAT, pipelines, fills, or building foundations, or were reported as and TOTAL_RELI (Table 1)]. The spatial extent of each landslide being active in geotechnical reports (see Appendix), were polygon, given in ft2, km2, and acres, was determined with the recorded as ‘active’. In wooded settings, identified landslides aid of ArcView [see database fields AREA_FT, AREA_KM, and that appeared to disrupt forest vegetation were classified as ACRES (Table 1)]. Approximate slope angles for each landslide ‘active’ if movement was known or estimated to have occurred were determined in the field and (or) from a slope map for the less than ten years before the date of landslide identification, or study area derived from the 10 m DEM and recorded to the as ‘dormant–young’ if movement was estimated to have occurred nearest 5 degrees (Fig. 8) [see database fields SI_FIELD, SS_ more than ten years before landslide identification. Landslides FIELD, SHS_FIELD, SBS_FIELD, STS_FIELD, and RS_GIS exhibiting indicators such as fresh scarp surfaces devoid of (Table 1)]. The watershed administrative unit, hydrologic basin, vegetation, back-titled trees, and open cracks in the ground were and water resource inventory area within which each landslide assigned both a ‘definite’ certainty rating and an ‘active’ activity is located was determined by using GIS overlay operations rating. If part of a deep-seated landslide showed evidence of between DNR hydrologic spatial coverages and the shapefiles recent movement either in the field or from geotechnical reports, ccuc_deep_seated_landslides.shp and ccuc_shallow_landslides. the entire landslide was classified as ‘active’, even though other shp [see database fieldsWAU , BASIN, and WRIA (Table 1)]. parts of that landslide may not presently be active. Landslides for Contiguous slopes where landslide activity was common, which there was convincing geomorphic field evidence for their but individual slides were too small to map, were classified as existence, but no evidence for recent movement, were classified ‘potentially unstable slopes’. In addition, slopes where landslide as having ‘definite’ or ‘probable’ certainty and ‘dormant–mature’ activity was not obvious, but that qualitatively appeared to have a or ‘dormant–relict’ activity, based upon a qualitative assessment high probability of failure due to steepness, underlying geologic of the geomorphic indicators of movement history, including unit, and structural attitude of bedding planes, were also included the nature of the vegetation growing on the landslide and the in the ‘potentially unstable slopes’ category. Potentially unstable distinctness of landslide features such as the crown-to-scarp slope transition (Fig. 5b). The majority of landslides that were not field checked were given ratings of ‘questionable’ certainty and SS ‘dormant–relict’ activity; however, those that exhibited distinct RS SBS original ground and (or) numerous large-scale indicators of landslide activity, as surface SI identified during review of the aerial photographs, were assigned SHS higher certainty and activity ratings (Fig. 7). Landslides that were identified during the photo reconnaissance phase of the project STS but not verified in the field are indicated as such in the database [see database fieldFIELD_VERI (Table 1)]. Digital photographs were taken of many of the landslides in an effort to show the landslide feature or to highlight specific parts of the landslide [see database fields DP_1 and DP_1_ DESCRIPTION to DP_5 and DP_5_DESCRIPTION (Table 1)]. EXPLANATION A digital archive of more than 475 photographs is included with SI Overall average slope gradient this report. It is intended that this photo archive will serve as SS Slope gradient of the scarp region one means by which landslide activity through time may be SHS Slope gradient of the head region monitored in the study area. SBS Slope gradient of the body region STS Slope gradient of the toe region RS Approximate average range of slope values for Compilation of GIS Inventory and Database the slope upon which the landslide is developed Landslide features and potentially unstable slopes that were Figure 8. Slope gradients used in the inventory database. Gradients verified in the field, or for which there was a preponderance are measured in degrees from the horizontal. All slope gradients were determined in the field utilizing a hand-held optical reading clinometer, of evidence supporting their existence from aerial photograph with the exception of the regional slope measurement (RS), which was reconnaissance alone, were digitized freehand in ESRI ArcView determined in ArcView through the use of a slope grid derived from 10 m GIS software on a base of 1996 DNR rectified digital orthophotos U.S. Geological Survey digital elevation models. See inventory database with a pixel resolution of 3 ft and a photo location accuracy of 20 fields SI_FIELD, SS_FIELD, SHS_FIELD, SBS_FIELD, STS_FIELD, and RS_GIS (Table 1). 10 REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON 11

slopes are considered likely to respond to slope modification reconnaissance were verified in the field. Of those, nearly 20 (such as drainage, grading, mining, logging, etc.) via partial or percent exhibit evidence of movement within the past 10 years full failure. based upon visible and (or) reported damage to infrastructure and buildings, visible ground cracking and displacement of Results material downslope, and disturbance of hillslope vegetation. Although landsliding is generally constrained to steeper slopes, A total of 825 landslides (593 deep-seated and 232 shallow), 80 slide movement has been documented on slopes with gradients percent of which were not previously mapped, are identified in as low as about 10 percent (6°). 2 this inventory across 260 mi of urbanizing lands in the Cowlitz The dominant form of deep-seated landslide movement in County urban corridor (Figs. 1, 3). Of the 232 shallow landslides, the study area is slow, rotational to translational rock and (or) 230 are classified as either active or dormant–young; of the 593 earth sliding, accounting for 86 percent of slides. The direction deep-seated slides, 127 show evidence of recent activity, 35 of landslide movement is fairly evenly distributed across the are considered dormant–young, 101 are considered dormant– study area, with a slight bias towards slopes with southerly to mature, and 330 are interpreted as being dormant–relict (Fig. southwesterly aspects. 7). Landslides range in size from 0.03 to 410 acres and 0.005 Deep-seated and shallow landslides occur within all rock to 2.5 acres for deep-seated and shallow types, respectively. units (Fig. 9) regardless of age. They are found within volcanic Cumulatively, identified landslides account for nearly 18 and sedimentary bedrock, within weakly consolidated to 2 2 mi (11,425 acres or > 46 km ), or 8.1 percent of the sloping unconsolidated fluvial and preexisting landslide deposits, and at lands (> 5°) within the study area (Fig. 3). Approximately 70 the interface between the two. Analysis of the areal distribution percent of the landslides initially identified in aerial-photograph of landslides indicates that per unit area, deeply weathered volcanic tuffs and certain sedimentary rocks (Toutle, Troutdale, Approximate and Cowlitz Formations and the Sandy River Mudstone ) age (Ma) SURFICIAL DEPOSITS (Evarts, 2002, 2004), as well as preexisting Quaternary 0 landslide deposits, are the most prone to slope failure (Fig. 10). Holocene Qa In comparison, units such as the Wilkes Formation, Eocene to Ql 0.015 Qfd Qls Miocene volcanic flows (including the Columbia River Basalt QUATERNARY Group), and the Grays River volcanics of Wells (1981) have a Qgo 0.050 Pleistocene low ratio of landslide area relative to the proportion of the study

Unconformity area underlain by these units, and thus are considered more 1.8 stable rock types (Fig. 10). Pliocene Ttf and Miocene? Pliocene? Tsr 30 30 and Miocene Percent of total landslide area Unconformity 25 originating from geologic unit 25

BEDROCK—VOLCANIC AND SEDIMENTARY ROCKS 20 Percent of total study area 20 underlain by geologic unit 5.3 Tw 15 15 13 Unconformity Miocene 10 10 Tcrb 5 5

TERTIARY Percent of total study area 17 Unconformity Percent of total landslide area 0 0 Oligocene

34 Tt lahars deposits alluvium (Missoula) preexisting volcanic tuffs flood deposits volcanic flows

Tgvs glacial outwash

36 Goble Formation Goble Formation Goble Formation Toutle Formation landslide deposits Wilkes Formation Cowlitz Formation

Tgvf Tgvt volcaniclastic rocks Group volcanic rocks

Eocene Grays River volcanics Columbia River Basalt Sandy River Mudstone) Troutdale Formation (and Figure 10. Comparative graph of the relationship between the percent 40 Tgrv Tc of total landslide area originating from a given geologic unit and the percent of the total study area underlain by that geologic unit. Volcanic tuffs, the Toutle, Troutdale, and Cowlitz Formations, and preexisting landslide EXPLANATION deposits have the highest ratio of landslide area relative to the area un- Qa alluvium Tcrb Columbia River Basalt Group flows derlain by these geologic units and thus are the most landslide-prone Ql lahar deposits Tt Toutle Formation geologic units in the study area. Qls landslide deposits Tgvf Goble Formation volcanic flows Qfd Missoula glacial outburst flood deposits Tgvt Goble Formation volcanic tuffs Qgo glacial outwash deposits Tgvs Goble Formation volcaniclastic Ttf Troutdale Formation sedimentary rocks 2. Geologic mapping by Evarts (2002, 2004) in the study area Tsr Sandy River Mudstone Tc Cowlitz Formation differentiated the Sandy River Mudstone from the Troutdale Formation, Tw Wilkes Formation Tgrv Grays River volcanics of Wells (1981) a distinction not recognized by previous geologic mapping (Wilkinson and others, 1946; Phillips, 1987b). Because this work was begun prior Figure 9. Generalized stratigraphic correlation diagram for the Cowlitz to publication of Evarts’ Deer Island and Woodland geologic quadrangle County urban corridor landslide study area (modified from Evarts, 2002 maps, the areas mapped as Sandy River Mudstone by Evarts are here and Walsh and others, 1987). incorporated into the Troutdale Formation. 12 REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON 13

Discussion bedrock-dominated landslides have initiated along such features (Fig. 14). East of the Cowlitz River, many slides appear to Geologic Controls initiate within or at the contacts of deeply weathered clay-rich Geologic factors such as rock type, degree of weathering, and Eocene pyroclastic beds (Fig. 15) (Evarts, 2002). North and west the presence of geologic structures (such as folds, faults, or of Kelso, the Cowlitz Formation crops out extensively (Roberts, fractures) can have a strong influence on the spatial and temporal 1958; Livingston, 1966; Evarts, 2001; McCutcheon, 2004). distribution of mass movement across a landscape. Several Many of the large and small deep-seated slides are moving within geologic factors identified in this study area appear to account the Cowlitz Formation, especially where the structural dip of the for the spatial distribution of many of the identified landslides. commonly deeply weathered shallow-marine sedimentary rocks The Pacific Northwest has experienced a relatively mild and is slope-parallel (Fig. 16). Along the Toutle River corridor, the wet climate throughout most of the Cenozoic Era (Wolfe, 1978). Toutle Formation (Roberts, 1958; Evarts, 2001), characterized by In addition, much of southwestern Washington, including the well-bedded and poorly sorted volcanic conglomerate, sandstone, study area, was not glaciated during the Pleistocene Epoch. As a siltstone, and claystone, hosts some spectacular landslides result, deep chemical weathering and relatively minimal physical (Fig. 17). Landslides initiating within the Toutle Formation erosion of the geologic materials have occurred (Thorsen, are particularly well-developed where Eocene andesitic flows 1989; Evarts, 2002). These processes have created saprolitic overlie deeply weathered siltstone and claystone facies. West of soils (in-situ deeply weathered bedrock), locally 30 ft thick, the Cowlitz River, sedimentary interbeds associated with flows formed by the weathering of Eocene to Miocene sedimentary of the Columbia River Basalt Group seem especially prone to and volcanic rocks (Figs. 9, 11, 12) and weakly consolidated to large-scale slope movement. Many of the large deep-seated unconsolidated Miocene to Quaternary sedimentary rocks and landslides found around the margins of the Columbia Heights Quaternary surficial deposits (Evarts, 2002) (Figs. 9, 13). These area north and west of Longview (Fig. 3) appear to have initiated deeply weathered deposits have been found to be especially at the contact between a deeply weathered sedimentary interbed prone to landsliding. and overlying basalt flows (McCutcheon, 2004) (Fig. 18). Extensive parts of the study area are underlain by Tertiary Miocene to Quaternary surficial alluvial deposits of the sedimentary (of both volcanic and nonvolcanic origin) and ancestral Columbia River form dissected terraces along the lower volcanic rocks containing inherent weaknesses, such as dipping slopes of the study area, filling in paleotopography developed bedding planes, joints (Fig. 6B), faults, brecciation and shear zones, on the underlying Tertiary bedrock. As noted by Evarts (2002, paleoweathering (paleosol) surfaces, and clay-rich interbeds. 2004), the non-volcaniclastic sedimentary units in the study area Although difficult to field-verify, I believe that many ofthe are particularly prone to landslide movement, with many areas underlain by them displaying evidence of small slumps and debris flows (Fig. 13). Many of these surficial deposits have weathered almost entirely to high-plasticity clays (for example, Sandy River Mudstone and Troutdale Formation; Livingston, 1966; Fiksdal, 1973; GeoEngineers, 1998; Evarts, 2002, 2004). As a result, numerous slides have developed on slopes underlain by these weakly consolidated sedimentary rocks (Figs. 19, 20) and along terraces formed by unconsolidated deposits of cataclysmic flood events (Missoula flood deposits) (Evarts, 2002) (Fig. 21).

Figure 11. Deeply weathered (saprolitic) volcaniclastic Figure 12. Deeply weathered (saprolitic) volcanic tuff of the Goble Formation ex- sandstone and conglomerate of the Goble Formation exposed in a roadcut along Bella Vista Road (NE¼ NW¼ sec. 21, T7N R1W). This posed in a roadcut along Bodine Road (SW¼ SE¼ sec. 9, outcrop is typical of volcanic tuff bedrock exposed throughout the study area. A sig- T7N R1W). Approximately 3 ft of reddish brown sandstone is nificant proportion of the landslides in the study area seem to have their surfaces of overlain by an estimated 10 ft of brownish yellow pebble con- rupture within deeply weathered volcanic tuff such as seen in this roadcut. The left glomerate. Deeply weathered volcaniclastic sediments such inset shows maroon-colored slightly sticky and very plastic brecciated deeply weath- as these are prone to slope failure, as seen along Bodine ered volcanic tuff. Fractures are now filled with white clay or zeolitic (?) material. The Road where undercutting of the adjacent slope has exposed right inset shows tan to yellow-brown, moderately sticky to highly plastic saprolitized this rock type in small roadcut failures. The rock hammer in volcanic tuff. The contact between the two different-colored units is believed to be the photo is 11 in. long. conformable. The rock hammer in both inset photographs is 11 in. long. 12 REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON 13

A B

Figure 13. Cross-bedded and lenticular sandstone of the Sandy River Mudstone. Typical sandstone exposures are light to medium gray and moderately friable where fresh, weathering to orange-brown. Features such as crossbedding and cut-and-fill structures A( ) indicate a fluvial depositional environment, and the mineralogy suggests a Columbia River provenance for the sand. This formation is mapped by Evarts (2002, 2004) in the Deer Island and Woodland 7.5-minute quadrangles as underlying a discontinuous surface along the east side of the Columbia River up to an elevation of 500 ft, and generally lying stratigraphically beneath coarser-grained fluvial deposits of the Troutdale Formation. This unit may correlate with the lower member of the Troutdale Formation of Mundorff (1964). A. Sloughed roadcut exposure along an abandoned logging road (NE¼SE¼ sec. 2, T5N R1W) exposing well-sorted medium-grained trough cross-bedded sandstone at an elevation of about 400 ft; outcrop height is about 15 ft. B. Plane-bedded medium-grained sandstone of the Sandy River Mudstone as exposed in a small roadcut failure along the lower reaches of Martin Bluff Road (SE¼NW¼ sec. 34, T6N R1W). Many landslides in the study area appear to be failing in Sandy River Mudstone and overlying Troutdale sediments.

main scarp location of B pipeline A right-of-way Figure 14. Large slow-moving deep-seated rock slide along the north side of the Kalama River (NE¼ sec. 33, T7N R1W), illustrating a large- scale bedrock landslide. This 90-acre landslide (GIS_ID 31) initiated in interbedded Goble Formation volcanic and volcaniclastic rocks. A. View Goble Formation basaltic andesite slide body to the north across the Kalama River valley. In 1996, renewed movement flows and flow breccias of the upper part of this slide complex ruptured and ignited a natural gas pipeline routed across the landslide. B. View to the southwest from the top of the landslide scarp. Goble Formation basaltic andesite flows and flow breccias are exposed in the main scarp. Several large bedrock landslides such as this one exist along the Kalama and Coweeman Rivers. C. Exposure of interbedded Goble Formation volcanic and volcaniclastic sedimentary rocks off Cloverdale Road (SW¼ sec 17, T6N R1W). Clay- rich volcaniclastic mudstone and siltstone are overlain by volcanic breccia (possibly basal flow breccia) and a basaltic-andesite flow (10–16 ft thick). The failure planes for some of the large deep-seated bedrock landslides in the study area, such as in A, may be at the contact of, or within, clay-rich volcaniclastic interbeds like the lowermost unit shown here.

B scarp C scarp basaltic andesite flow

volcanic breccia (basal flow breccia?)

slide body basaltic clay-rich volcaniclastic andesite flows mudstone and siltstone 14 REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON 15

Figure 15. Contorted foundation of a house destroyed by a landslide developed within deeply weathered volcaniclastic rocks of the Goble For- mation. The view is to the southeast. This house, off Pin Creek Lane near Carrolls, was destroyed in 1996 by the reactivation of a 6-acre rotational B rock slide–flow (GIS_ID 194) approximately two weeks before construction was to be completed. (The structure was subsequently burned down to its foundation.) Inset shows an outcrop of deeply weathered saprolitic volcaniclastic rock consisting of medium-grained sandstone and fine- grained ash-rich siltstone. This rock has been altered to low-permeability, very sticky, very plastic, low-shear-strength clays. It is in such rock units that this and many other landslides within the study area are moving. The rock hammer is 11 in. long. C Figure 16. (above right) Small rotational deep-seated landslide (GIS_ID 505) failing in weathered sediments of the Cowlitz Formation along Colum- bia Heights Road (sec. 5, T8N R2W). This landslide may have initiated in response to cutting at the toe of the slope for Columbia Heights Road. A. View west-northwest from the top of the landslide. Note the back-rotation of 3 feet the fence post, the discrete rotational blocks of the landslide, and small internal scarps. Also note Columbia Heights Road at the toe of the slide B. View south from Columbia Heights road, where the road intersects the landslide. Note the hummocky nature of the slide, and the deep red colors associated with deeply weathered sediments of the Cowlitz Formation. The landslide initiated where the bedding attitude of the Cowlitz Formation (N81°E, 11°NW) intersects the roadcut at the maximum dip-angle of the sediments. C. Outcrop of nearby Cowlitz Formation sediments. These sediments have been deeply weathered (to saprolite) and altered to high-plasticity, very sticky clays, which are very prone to landsliding, especially where the structural dip of the sedimentary layering is near-parallel to the sloping ground surface. When this occurs, failure or slip planes develop along weak, clay-rich layers.

A EXPLANATION B Beigle Mountain Beigle Mtn. landslide complex landslide scarp generalized direction of slide movement

Beigle Toutle River Mountain 1980 lahar deposit C direction of view in

SR 504

North Fork Toutle River main scarp

Toutle River lateral pressure ridges SR 504 sag pond 0 1000 2000 ft C 14 REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON 15

A B Columbia Heights Columbia Heights main scarp C C

EXPLANATION Columbia Heights landslide D landslide scarp generalized direction of slide movement D C approximate photograph location 0 1000 ft

C D

Figure 18. Dormant–relict deep-seated rotational to translational Columbia Heights landslide [GIS_ID 504] (sec. 17, T8N R2W). The scarp exposes basalt flows of the Saddle Mountains Basalt of the Columbia River Basalt Group. A sedimentary interbed within the basalt, as well as the Cowlitz For- mation (not shown on photographs), crop out stratigraphically beneath the Saddle Mountains Basalt. I believe that the failure plane for this landslide is developed at the contact or within this sedimentary interbed or the Cowlitz Formation. Landsliding of this type, involving a cap of Columbia River Basalt underlain by weak sedimentary rocks, is common north and west of Longview. Other large deep-seated landslides with similar failure mechanisms include GIS_ID 480, 481, 483, 516, 533, 538, 539, 554, 558, 576, and 590. A. Shaded-relief topographic map of the Columbia Heights landslide. B. Aerial photograph of the landslide looking to the north-northwest. Note the general ‘flow-topography’ associated with the landslide body, incised drainages along the slide margin, and a distinct, near-vertical main scarp. C. Main scarp of the landslide, an approximately 100 ft high near-vertical cliff of basalt. Geologic mapping confirms that weak sedimentary units crop out beneath the basalt flow exposed in the scarp of the landslide (McCutcheon, 2004). Many landslides developed in geologic settings similar to this one also display near-vertical main scarps (cliffs) in basalt flows. D. Large boulders of basalt exposed in a small over-grown quarry in the lower part of the landslide. Note person in upper right corner of photo for scale. The only source for these large basaltic boulders is the outcrops of basalt above the main scarp of the landslide; they were transported to their current location by movement of this landslide.

Figure 17. (facing page, bottom) Dormant Beigle Mountain landslide complex [GIS_ID 337], located northeast of Toutle (secs. 17, 18, 19, 20 T10N R1E). This and other large deep-seated landslides along the Toutle River corridor are failing in deeply weathered and altered sediments of the Toutle Formation (Roberts, 1958; Evarts, 2001). Other large deep-seated landslides in this unit include slides GIS_ID 320, 325, 330, and 336. SR, State Route. A. Shaded-relief topographic map of the Beigle Mountain landslide complex. The landslide is developed along a bend in the Toutle River, just downstream of the confluence between the north and south forks. Initial slide movement may have resulted from undercutting of the slope by the river. The western part of the landslide appears more hummocky because it was clearcut logged several years prior to the production of the base topographic map, allowing for a more accurate representation of the slide topography for that part of the slide. The eastern half of the landslide has recently been logged and is equally as hummocky. B. Aerial photograph of the landslide complex, looking from the south-southeast. Photograph C looks across the clearcut visible in the northeast part of the slide complex. C. View to the east-northeast from the main scarp near Beigle Mountain. The direction of slide movement is to the southeast, towards the Toutle River. Note the steep main scarp, lateral pressure ridges (which have formed perpendicular to the direction of slide movement), and the sag pond, all indicators of slide activity. 16 REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON 17

A SW ground surface and approximate NE location of failure suface (Dec. 1998)

GeoEngineers approximate location of failure surface (June 1998) boring 5 location of B 400 upper 400 Troutdale ground surface (June 1998) lower Fm. Troutdale GeoEngineers Fm. boring 9 GeoEngineers older boring 2 GeoEngineers 200 slide 200 debris boring 1 Elevation (feet)

0 200 feet Cowlitz Formation

0 0 Figure 19. Geologic controls on the Aldercrest–Banyon landslide (GIS_ID A. B C 272). Generalized geologic cross sec- gravel facies of the Troutdale Formation tion (modified from GeoEngineers, 1998; ~75 feet see Fig. 4 for location). This interpretation indicates that the recent landslide is a reactivation of an older slide, and exploratory geotechnical drilling has revealed that the failure plane is at or near the contact of fluvial sediments of the Troutdale Formation micaceous sandstone of the Cowlitz Formation and (or) older slide debris with sedimentary rocks of the Cowlitz Formation (GeoEngi- neers, 1998). B. View to the south from the base of the approximately 75 ft high main scarp, exposing fluvial gravels and sands of the Troutdale Formation. C. Roadcut exposure off Carroll Road (SW¼SE¼ sec. 1, T7N R2W) that exposes the contact between fluvial gravels of the Troutdale Formation and underlying deeply weathered (saprolitic) sandstones of the Cowlitz Formation. I believe that the Aldercrest–Banyon and many other landslides in the study area initiated at the contact between these two formations.

A B Figure 20. Kelso “K” small deep-seated "K" earth slide–flow [GIS_ID 422], which initiated in fluvial silts and clays of the Troutdale Formation (sec. 26, T8N R2W) and was reactivated in 2002. The contact between the Troutdale and underlying Cowlitz Formations is exposed a short distance away, and may be the locus for movement of this slide. A. Hillslope prior to the 2002 reactivation, looking north. The gabion wall at the base of the slope was put in place as a toe buttress for a small pre-2002 landslide. B. View from nearly the same vantage point as in A as it appeared shortly after early 2002 reactiva- 16th Ave. and Crawford St. tion. The toe of the slide pushed up against C the northeast corner of the nearby motel. C. View of the landslide from the north side of the motel, looking towards the east. The intersection of 16th Avenue and Crawford Street is at the top of the landslide. The landslide reactivated after a period of heavy precipitation. Note the destruction of the gabion wall and the damage to the northeast corner of the motel, caused by the impact of falling trees pushed over by the slide movement. In the months following the landslide, both the toe and main scarp area were geotechni- cally remediated. 16 REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON 17

Landslide Types The dominant form of landsliding within the study area is the extremely slow to moderate rotational to translational earth and (or) rock slide composed of extensively weathered bedrock and (or) surficial deposits (for example, Figs. 12, 16, 19). Faster- moving rock falls, topples, and shallow colluvial slides and debris flows are generally limited to the inner gorges of the Kalama and Coweeman Rivers, the Columbia River bluffs west of Longview, steep tributary drainages, and the rocky headscarps of some of the larger rock-slide complexes (Figs. 6, 22) (Wegmann and Walsh, 2001). Many of the larger landslides appear to have sporadic movement histories, as exhibited by recently reactivated parts of deep-seated slides such as the Aldercrest–Banyon landslide (GIS_ID 271, 272) (Figs. 4, 19), where only part of the larger landslide feature has been reactivated. A number of smaller Figure 21. View to the east of a small deep-seated translational earth active slides have been identified within the confines of larger slide–flow north of Woodland (GIS_ID 95) (S½ sec. 47, T5N R1E). The dormant landslides; for example, the Davis Terrace landslide landslide initiated in fine-grained Pleistocene Missoula flood deposits. (GIS_ID 264) in southeast Kelso (Gerstel and Brunengo, 1994) Slackwater deposits constitute terraces along the Columbia River and its is mapped as a large, predominantly dormant, deep-seated tributaries with surface elevations of 200 to 250 ft (Evarts, 2002, 2004). Missoula flood deposit terraces north and east of Woodland are prone slide with many small, active superimposed slides (Fig. 23). to small landslides such as this one. The top of the slide extends east This relationship of smaller active landslides superimposed on to Woodland View Drive. Alders and cottonwoods are revegetating the larger dormant features may indicate that the large deep-seated landslide body (delineated by dashed white line). Movement of this slide landslides found within the study area commonly are composite during the second half of the 1990s damaged a structure at the base of the slope (later removed). The inset depicts an outcrop of unconsolidated features that are not necessarily active in totality, but rather tend Missoula flood deposits of rhythmically bedded plastic silty clay (thin gray to move as smaller distinct landslides that collectively compose layers) and fine sand. Note the granitic dropstone (above knife), inter- a much larger area of deep-seated landslide movement. preted as having melted out of a flood-transported iceberg, suggesting a cataclysmic flood origin for these deposits. The knife is 8 in. long.

A recent rock fall scar B

276 Coweeman R. 274 312 Davis Terrace location of landslide complex Aldercrest–Banyon 273 landslide

313 275

314 divots C 315 267 EXPLANATION 266 active deep-seated 316 landslide 268 Davis Terrace Figure 22. Small recent rock fall within landslide complex Coweeman R. a larger dormant–young rock fall–slide lo- active landslide 265 cated above State Route 4, approximately scarp 0.5 mi east of Stella (GIS_ID 583) (sec. landslide scarp generalized direction 7, T8N R3W). This rock fall began on a of slide movement 1000 ft cliff along the north side of the Columbia A. Figure 23. River in Columbia River Basalt. View 1 foot Distribution of active landslides (in red, to the north looking upslope at the main showing GIS_ID) superimposed on the Davis Terrace scarp and the location of the recent rock landslide complex (GIS_ID 264) (in blue) (secs. 25 and fall initiation. B. Rocks impounded on the 35, T7N R2W; secs. 1 and 2, T8N R2W). Many of the uphill side of a maple tree beneath the larger deep-seated landslides within the study area slide run-out area. C. Divots or indentations in the pavement of State Route 4, indicat- probably move by partial reactivation as smaller slides ing the impact spots for rocks from the failure area 500 ft upslope. such as these, rather than moving as a single mass. 18 REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON 19

Possible Triggering Mechanisms Chappell, 2001). The Columbia River and its major tributaries It is beyond the scope of this report to assign specific triggering were graded to this lower sea level during glacial times. This mechanisms to individual landslides in the inventory. However, resulted in incision of the Columbia and tributary valleys, several potential mechanisms seem possible for the majority of including the lower parts of the Cowlitz, Coweeman, Kalama, deep-seated landslides in the study area. and Lewis Rivers, and oversteepening of lower valley slopes. The steepening of lower valley slopes destabilized parts of Natural Causes the landscape, which responded by landsliding as a means to reestablish slope equilibrium. Movement of many of the landslides identified in this study seems to have been prompted by natural causes. The primary Human Activities initiating factor behind many currently active landslides appears to have been climatically driven increases in ground-water levels Some of the landslides classified as active have been influenced and soil pore-water pressures (Shannon & Wilson, 1965; Fiksdal, by human activities (Fig. 24). Land-use modifications can alter 1973; Thorsen, 1989; Harp and others, 1998; GeoEngineers, the amount and flow direction of surface and ground water on 1998; Burns and others, 1999; Robison and others, 1999; slopes, and the balance of gravitational and resisting forces Chleborad, 2000) (see Fig. 2). Therefore, it is assumed that many through changes in slope configuration. Such anthropogenic of the currently dormant deep-seated landslides in the study slope modifications may in turn initiate landslide movement area also were triggered by past increases in precipitation and (Koloski, 1998; Shannon & Wilson, 2000). Sidle and others ground-water levels. However, reactivation of dormant deep- (1985) suggested that residential development of hillslopes seated landslides does not necessarily occur every time higher- can decrease slope stability in the following ways: (1) removal than-normal precipitation amounts occur. Landslide-specific of support by excavation, (2) mechanical overloading by fill thresholds must be crossed before an individual slide will move, placement, (3) concentration of water on the site and (or) the and previous movement may increase or decrease thresholds introduction of additional water, and (4) extensive removal or (such as requirements for ground-water level or soil pore-water conversion of native vegetation. All of these activities were pressure) for a particular slide. The undercutting of the base of observed to occur at various degrees of severity on residential a slope by erosion along the larger rivers and streams within the hillslopes within the study area. Activities such as the removal of study area may also have initiated both small- and large-scale vegetation, grading of surficial deposits, undercutting of slopes for roads, quarries, pipelines, and building emplacements, and slope movements (for example, landslide GIS_ID 20, Fig. 6a). Some of the dormant deep-seated landslides may have other construction projects may have singularly, or in some been seismically induced (Wieczorek, 1996). During the 1949 instances collectively, contributed to recent landsliding in magnitude 7.1 Olympia earthquake, for example, rock falls and the study area (Figs. 20, 24). Human development upon large earth slides were reported within the study area inactive deep-seated landslides may be a contributing factor (Chleborad and Schuster, 1998). It stands to reason that if a moderate to great earthquake were to occur close to the study area—such as could be produced by the nearby Cascadia subduction zone, which is capable of producing earthquakes up to about magnitude 9.0 (Atwater abandoned petroleum and Hemphill-Haley, 1997)—landsliding would pipeline alignment very likely result, especially if it were to occur during the wet season when ground-water and soil-moisture levels were elevated. Dormant–relict landslides found along lower slopes of the Columbia River valley and its tributaries may have been triggered by the rapid drawdown of floodwaters during the waning clay-rich diamicton (older landslide debris derived stages of individual cataclysmic Missoula flood from the Troutdale Formation) events (Wieczorek, 1996; Wegmann and Walsh, 2001). Localized oversteepening of the walls of Figure 24. View to the northwest of a human-induced, small deep-seated rotational earth the Columbia River valley below approximately slide-earth flow north of Kalama along Spencer Creek Road (GIS_ID 133) (NE1/4 sec. 8, T6N R1W). The slide is about 75 ft wide by 40 ft long and 15 ft deep. The slide initiated in a 240 ft in elevation (the maximum elevation of clay-rich diamicton derived from the Troutdale Formation, and is an example of a slide that is the late Pleistocene Missoula glacial outburst moving within younger unconsolidated surficial deposits. This landslide began moving after floods) may also have occurred as a result of a period of heavy rain in spring 2000. The slope had recently been cut back to enlarge a the floods, which in turn might have caused an private yard, resulting in a lack of lateral support for the lower part of the slope. Fortunately, a pipeline that had transported liquid petroleum products, located only a few feet uphill from increase in landslide activity along the slopes. In the scarp of the landslide, was abandoned several years prior to this event, in favor of a new addition to the erosive effects of Missoula flood route that bypasses the larger landslide feature (GIS_ID 4) on which this landslide sits. In events, global sea level was approximately 400 1996, movement of part of the larger landslide, a short distance to the north of the landslide ft lower during full glacial conditions (~20,000 depicted here, resulted in a small crack in the pipeline with a resultant release of fuel (Geo- Engineers, 1996). The small landslide in the photo illustrates that human action at the base years ago) than it is today (Lambeck and of slopes may decrease the overall stability of a slope. 18 REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON 19

to their reactivation (Gerstel and Brunengo, 1994). However, that feature was digitized and incorporated into the database. because human modification of hillslopes in the study area is Viewing individual polygons at scales larger than the digitization quite common and only a small proportion of these slopes show scale may produce unwarranted levels of confidence in the evidence for recent landslide movement, the primary landslide boundary locations of the polygon. The database field LINE_ triggering factor is likely related to natural causes. TYPE specifies the certainty of landslide boundary or scarp line Whenever minor amounts of movement occur within a locations (Table 1). It is important to note that the actual on- large deep-seated slide in developed areas, underground water the-ground locations of landslide margins and their associated and sewer lines may be disrupted, as at the Aldercrest–Banyon geomorphic features may vary by up to several hundred feet landslide (Buss and others, 2000), resulting in the potential from the locations represented in this inventory. All attempts addition of large quantities of water to the slide mass. Septic were made to faithfully represent the spatial locations of tanks, lawn watering, and the collection of storm-water runoff landslides and their features; however, due to the uncertainties from streets, driveways, and roofs may also increase the amount listed above, some degree of caution is warranted when using of water present within a landslide mass over what would have the inventory for precise location purposes. Also, the modeled existed under undeveloped conditions. This addition of extra potentially unstable slope areas included in the inventory (see water to a hillslope may be a factor in the triggering and (or) ESRI shapefileccuc_potentially_unstable_slopes.shp ) may vary enhanced movement of naturally triggered landslides. from their actual on-the-ground extent. In a number of cases, it may have been the combination This inventory is intended to serve for general planning of slope modification by humans and an increase in regional purposes only. Under no circumstances should this inventory precipitation levels (such as occurred during the late 1990s) that and database be used for landslide characterization in lieu of resulted in the triggering of recent (active) landslides identified site-specific studies by qualified professionals. in this study. If this is true, it can be expected that the urbanizing areas of Cowlitz County will suffer an increased rate of landslide Potential uses activities during future periods of prolonged above-average precipitation. This landslide report and inventory provides insight into current and future potential landslide problem areas. Because landslides tend to recur in the same location, this inventory will Inventory limitations provide planners with a screening tool showing the geographic This inventory identifies landslides and geologic and geomorphic distribution of known and potential landslide areas within the conditions prone to landsliding within the Cowlitz County Cowlitz County urban corridor, and serve as a useful aid in urban corridor. Although efforts were made to identify as many decision-making processes relating directly to requirements landslides as possible, omissions undoubtedly occurred. It is of the Growth Management Act and critical-areas protection assumed that with continued land clearing and development, ordinances. Although the landslide inventory is not intended and the future acquisition of aerial photography and Light or detailed enough for site-specific landslide investigations, it Detection and Ranging (lidar) data for the study area, previously should prove to be a useful tool for Cowlitz County and city unrecognized landslides will be identified. Additionally, the governments, private citizens, state and federal agencies, geologic boundaries of some of the landslides mapped for this inventory and engineering consultants, public and private utilities, land will have to be revised. A recent study in the central Puget Sound developers, and students who are interested in landslides and lowland comparing the effectiveness of landslide identification slope-stability issues in the urban corridor of Cowlitz County. A between traditional aerial-photograph and lidar methods found few of the foreseeable uses of the inventory are briefly described that lidar was much better suited to the accurate spatial location below. of large deep-seated slides (Gold, 2004). Limitations on spatial accuracy of the GIS polygons, lines, Planning and points include: (1) the variable accuracy of landslide feature By avoiding areas of known landslide potential, or by mitigating locations determined from reconnaissance and field verification the risk of damage, careful development of hillsides can reduce in heavily-forested terrain using 1:12,000-scale unrectified aerial economic and social losses resulting from slope movements. photos; (2) spatial errors produced during freehand digitization Landslide risk can be reduced by the following approaches: (1) of features onto 1996 rectified orthophotos; and (3) the inherent restricting development in landslide-prone areas; (2) developing spatial errors associated with the orthophotos, 1:24,000-scale and implementing improved codes for excavation, grading, topographic maps, and 10 m DEMs used for digitization and construction, and landscaping; (3) implementing remediation landslide elevation, slope, and length calculations (see individual measures to prevent or control landslides (controlling drainage, metadata files for horizontal and vertical spatial accuracy limiting slope-geometry modification, and designing appropriate information pertaining to each ESRI shapefile). Although all structures); and (4) developing warning systems and evacuation attempts were made to minimize the spatial errors associated routes (Kockelman, 1986). An important first step in a regional with the GIS polygon, line, and point features, errors undoubtedly landslide risk-reduction program is the identification of existing exist in the inventory. landslides as well as slopes which, due to the combination of I recommend that GIS maps produced using the ESRI geology, topography, and historical instability, are prone to shapefiles should be at a scale no greater than 1:12,000. For future landslide activity. Reliable landslide hazard maps are of each landslide polygon, the scale of digitization [see database significant value in establishing risk-reduction programs. Natural field DIGITIZATI (Table 1)] provides the map scale at which 20 REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON 21 slopes that are currently moving clearly have a high risk of alteration of natural slopes may also have contributed to the movement in the future, and previous landslide activity is often initiation of new slides as well as the reactivation of preexisting a very strong indicator for areas of future slope instability (as landslides. Although a majority of the slides in this inventory exemplified by the number of smaller active landslides identified are considered dormant features, the obvious recent reactivation within the mapped boundaries of larger dormant landslides in of parts of large previously dormant deep-seated slides such as this inventory; for example, see Figs. 4b, 6, 23). Thus, this report the Aldercrest–Banyon, Davis Terrace, Kalama River, Fallert and inventory of landslides establishes a framework from which Bridge, Alpha Drive, State Route 504, State Route 411, and Allen to evaluate where slope stability problems exist or may develop Brothers Drive landslides (see Fig. 3) serves as a reminder that in the future. Furthermore, this inventory can be expanded landslides are inherently unstable landforms, which are prone with updated information concerning the location of landslides to reactivate when driving and (or) resisting forces are altered within the study area, and will form the baseline for future slope- beyond threshold limits. stability analysis. Landslides such as the Aldercrest–Banyon slide serve as stark reminders of the potentially devastating consequences Hazard Map Calibration of human development on unstable slopes. As our population This inventory is a necessary step in the production of future expands beyond established urban areas, our need for new Cowlitz County urban corridor slope stability hazard zonation and updated geologic-hazard mapping increases in step. This maps. Careful identification of the distribution of existing landslide inventory provides a starting point from which to landslides will prove beneficial during the construction of assess slope stability-related issues within the Cowlitz County the maps, as this will allow for comparison of areas of actual urban corridor. This inventory is intended for planning-scale landslide occurrence to hazard zone designations for calibration studies, which hopefully will lead to successes in minimizing purposes. and mitigating landslide-related threats to public and private property and safety in Cowlitz County, Washington. Regional Analyses Acknowledgments This landslide inventory may be used with other inventories of southwest Washington and northwest Oregon (for example, Invaluable critical technical reviews of this report were provided Washington Department of Natural Resources, 1996; Burns by Wendy Gerstel, Matthew Brunengo, and H. Randy Sweet. I and others, 1998; Robison and others, 1999; Hofmeister, 2000) would like to acknowledge the field assistance received during to summarize regional trends in landslide location related to this project by Patrick Godsil, Andy Dunn, Sammantha Magsino, factors such as geologic unit, slope angle, slope aspect, bedrock and Ryan Gold. Russ Evarts provided valuable field time in structures, development practices, large single storm events, and order to develop a geologic picture of southwestern Washington anomalously wet periods. for me. Russ also provided many insights into landslide-prone rock units within the study area as well as draft copies of his Summary Silver Lake, Deer Island, and Woodland 7.5-minute geologic maps. The evolution of my knowledge regarding landslides This report provides a comprehensive, but not necessarily in southwestern Washington in relation to the geology has inclusive, inventory of landslides identified between February benefited immensely through discussions and field trips with 2000 and October 2002 within 260 mi2 of urbanizing lands in the Tim Walsh, Wendy Gerstel, Steve Palmer, Al Niem, Derek Cowlitz County urban corridor. The 825 identified landslides and Kleibacker, Mark McCutcheon, Russ Evarts, Pat Pringle, Chris their attributes are mapped in a GIS environment via eleven ESRI Johnson, Rex Hapala, Scott Burns, Jon Hofmeister, Randy shapefiles. Up to 82 specific characteristics for each landslide Sweet, Joe Dragovich, Matt Brunengo, Roy Garrison, and Carol are available in the ESRI database (.dbf) files, accessible with Serdar. George Bradford, formerly at the Cowlitz County GIS software such as Microsoft Excel or Access. Department, was instrumental to the initiation of the project. The dominant forms of landsliding within the study area Assistance in obtaining geotechnical reports and the location are extremely slow to moderate rotational to translational earth of known recent landslides was provided by the following and rock slides, composed of deeply weathered bedrock and (or) individuals: Sheldon Somers and Mike Wojtowicz (Cowlitz surficial deposits. Many of the Tertiary sedimentary and volcanic County Department of Building and Planning); Rich Iverson, rocks as well as Pliocene to Quaternary surficial sedimentary Mike Hubbard, Ryan Lapossa, and Larry Johnson (Cowlitz units have thick weathering profiles consisting of clays with County Department of Public Works); Sam Adams and Susan high plasticity and low yield strength, which have proven to be Eugenis (City of Kelso); Carl McCrary (City of Kalama); Rob especially prone to landsliding, particularly on steeper slopes. VanderZanden (City of Woodland); Roy Hewson, Ruth Bunch- Of the 825 landslides, approximately 20 percent show field Gipe, and Robert Millspaw (City of Longview); and Lynn Moses evidence of activity within the past 10 years, including slides (Washington State Department of Transportation). John Bright that have damaged homes and property, state, county, and city provided GIS technical support. Karen Meyers and Jari Roloff roads, natural gas and liquid petroleum pipelines, and bridges. I improved the text and figures through their editing and layout believe that many of the recently active slides can be attributed skills. to periodic multi-year increases in the regional precipitation amount (such as occurred during the latter 1990s), resulting in elevated groundwater and soil-moisture levels. Human 20 REPORT OF INVESTIGATIONS 35 LANDSLIDE INVENTORY OF COWLITZ COUNTY URBAN CORRIDOR, WASHINGTON 21

References cited GeoEngineers, Inc., 1998, Report—Geotechnical engineering services, slope failure evaluation, Aldercrest–Banyon Landslide, Kelso, Atwater, B. F.; Hemphill-Haley, Eileen, 1997, Recurrence intervals for Washington: GeoEngineers, Inc. [under contract to] City of Kelso, great earthquakes of the past 3,500 years at northeastern Willapa v. 1. Bay, Washington: U.S. Geological Survey Professional Paper 1576, 108 p. Gerstel, W. J., 1999, Deep-seated landslide inventory of the west- central Olympic Peninsula: Washington Division of Geology and Brunengo, M. J., 1994, Geologic hazards and the Growth Management Earth Resources Open File Report 99-2, 36 p., 2 plates. Act: Washington Geology, v. 22, no. 2, p. 4-10. Gerstel, W. J.; Brunengo, M. J., 1994, Mass wasting on the urban fringe: Burns, S. F., 1999, Aldercrest landslide, Kelso, Washington, engulfs Washington Geology, v. 22, no. 2, p. 11-17. subdivision [abstract]: Geological Society of America Abstracts with Programs, v. 31, no. 6, p. A-41. Gold, R. D., 2004, A comparative study of aerial photographs and LIDAR imagery for landslide detection in the Puget Lowland, Burns, S. F.; Burns, W. J.; James, D. H.; Hinkle, J. C., 1998, Landslides Washington: Washington Division of Geology and Earth Resources in the Portland, Oregon metropolitan area resulting from the storm Open File Report 2004-6, 66 p., 1 CD-ROM, 1 plate. [accessed of February 1996—Inventory map, database and evaluation: Mar. 9, 2004 at http://www.dnr.wa.gov/geology/pdf/ofr04-6.zip] Portland State University, Department of Geology, Portland, Oregon, 33 p. [accessed Aug. 11, 2005 at http://percy.geol.pdx.edu/ Harp, E. L.; Chleborad, A. F.; Schuster, R. L.; Cannon, S. H.; Reid, G425-FieldGIS/metrosld.doc] M. E.; Wilson, R. C., 1998, Landslides and landslide hazards in Washington State due to February 5–9, 1996 storm: U.S. Geological Burns, S. F.; Burns, W. J.; James, D. H.; Hinkle, J. C., 1999, Reactivation Survey Administrative Report, 1 v. [accessed Jan. 10, 2006 at http:// of ancient landslides in northwest Oregon and southwest Washington landslides.usgs.gov/learningeducation/docs/Wash_hrp.pdf] [abstract]: Association of Engineering Geologists, 42nd Annual Meeting, Program with Abstracts, p. 61. Hofmeister, R. J., 2000, Slope failures in Oregon—GIS inventory for three 1996/97 storm events: Oregon Department of Geology and Buss, K. G.; Benson, B. E.; Koloski, J. W., 2000, Aldercrest–Banyon Mineral Industries Special Paper 34, 20 p., 1 CD-ROM. landslide—Technical and social considerations [abstract]: AEG News, v. 43, no. 4, p. 78. Jackson, J. A., editor, 1997, Glossary of geology; 4th ed.: American Geological Institute, 769 p. Chleborad, A. F., 2000, Preliminary method for anticipating the occurrence of precipitation-induced landslides in Seattle, Kleibacker, D. W., 2001, Sequence stratigraphy and lithofacies of the Washington: U.S. Geological Survey Open-File Report 00-469, 29 middle Eocene upper McIntosh and Cowlitz Formations, geology p. of the Grays River volcanics, Castle Rock–Germany Creek area, southwest Washington: Oregon State University Master of Science Chleborad, A. F.; Schuster, R. L., 1998, Ground failure associated with thesis, 219 p., 1 CD-ROM, 3 plates. the Puget Sound region earthquakes of April 13, 1949, and April 29, 1965. In Rogers, A. M.; Walsh, T. J.; Kockelman, W. J.; Priest, Kockelman, W. J., 1986, Some techniques for reducing landslide G. R., editors, Assessing earthquake hazards and reducing risk in hazards: Bulletin of the Association of Engineering Geologists, v. the Pacific Northwest: U.S. Geological Survey Professional Paper 23, no. 1, p. 29-52. 1560, v. 2, p. 373-440. Koloski, Jon W., 1998, Humans as a geologic agent. In American Cruden, D. M.; Varnes, D. J., 1996, Landslide types and processes. In Society of Civil Engineers, Seattle Section; and others, Landslides Turner, A. K.; Schuster, R. L., editors, Landslides—Investigation in the Puget Sound region—Seminar: American Society of Civil and mitigation: National Academy Press; National Research Council Engineers, Seattle Section, [5 p., unpaginated]. Transportation Research Board Special Report 247, p. 36-75. Lambeck, Kurt; Chappell, John, 2001, Sea level change through the last Dragovich, J. D.; Brunengo, M. J., 1995, Landslide map and inventory, glacial cycle: Science, v. 292, no. 5517, p. 679-686. Tilton River–Mineral Creek area, Lewis County, Washington: Livingston, V. E., Jr., 1966, Geology and mineral resources of the Kelso– Washington Division of Geology and Earth Resources Open File Cathlamet area, Cowlitz and Wahkiakum Counties, Washington: Report 95-1, 165 p., 3 plates. Washington Division of Mines and Geology Bulletin 54, 110 p., Evarts, R. C., 2001, Geologic map of the Silver Lake quadrangle, Cowlitz 2 plates. County, Washington: U.S. Geological Survey Miscellaneous Field McCalpin, James, 1984, Preliminary age classification of landslides for Studies Map MF-2371, 1 sheet, scale 1:24,000, with 37 p. text. inventory mapping. In Engineering Geology and Soils Engineering Evarts, R. C., 2002, Geologic map of the Deer Island quadrangle, Symposium, 21st Annual, Proceedings: [Idaho Transportation Columbia County, Oregon and Cowlitz County, Washington: U.S. Department], p. 99-111. Geological Survey Miscellaneous Field Studies Map MF-2392, McCutcheon, M. S., 2004, Stratigraphy and sedimentology of the 45 p., 1 plate, scale 1:24,000. middle Eocene Cowlitz Formation, and adjacent sedimentary and Evarts, R. C., 2004, Geologic map of the Woodland quadrangle, Clark volcanic units in the Longview–Kelso area, southwest Washington: and Cowlitz Counties, Washington: U.S. Geological Survey Oregon State University Master of Science thesis, 327 p., 2 plates. Scientific Investigations Map SIM-2827, 1 sheet, scale 1:24,000, Myers, D. A., 1970, Availability of ground water in western Cowlitz with 38 p. text. County, Washington: Washington Department of Ecology Water- Fiksdal, A. J., 1973, Slope stability of the Longview–Kelso urban Supply Bulletin 35, 63 p., 2 plates. area, Cowlitz County: Washington Division of Geology and Earth Mundorff, M. J., 1964, Geology and ground-water conditions of Clark Resources Open File Report 73-2, 4 p., 2 plates. County, Washington, with a description of a major alluvial aquifer GeoEngineers, Inc., 1996, Landslide and erosion hazards evaluation; along the Columbia River: U.S. Geological Survey Water-Supply Existing pipeline route—milepost 165 to 248, southwest Paper 1600, 268 p., 3 plates. Washington: GeoEngineers, Inc. [under contract to] Olympic Phillips, W. M., compiler, 1987a, Geologic map of the Mount St. Helens Pipeline Company, 1 v. quadrangle, Washington and Oregon: Washington Division of Geology and Earth Resources Open File Report 87-4, 59 p., 1 plate, scale 1:100,000. 22 REPORT OF INVESTIGATIONS 35

Phillips, W. M., compiler, 1987b, Geologic map of the Vancouver Washington Department of Natural Resources, 1996, North Elochoman quadrangle, Washington: Washington Division of Geology and watershed analysis: Washington Department of Natural Resources, Earth Resources Open File Report 87-10, 27 p., 1 plate, scale 1 v. [accessed Apr. 25, 2005 at http://www.dnr.wa.gov/cgi-bin/ 1:100,000. wsasmt.cgi?wsaval=elochoman_north] Roberts, A. E., 1958, Geology and coal resources of the Toledo–Castle Washington Forest Practices Board, 2001, Washington forest practices— Rock district, Cowlitz and Lewis Counties, Washington: U.S. Rules, WAC 222; Board manual; Forest Practices Act RCW 76.09: Geological Survey Bulletin 1062, 71 p., 6 plates. Washington Forest Practices Board, 1 v. [accessed on Aug. 11, 2005 Robison, E. G.; Mills, K. A.; Paul, Jim; Dent, Liz; Skaugset, Arne, at http://www.dnr.wa.gov/forestpractices/rules/] 1999, Storm impacts and landslides of 1996—Final report: Oregon Wegmann, K. W., 2003, Digital landslide inventory for the Cowlitz Department of Forestry Forest Practices Technical Report 4, 145 County urban corridor—Kelso to Woodland (Coweeman River to p. Lewis River), Cowlitz County, Washington: Washington Division Schuster, R. L., 1996, Socioeconomic significance of landslides. In of Geology and Earth Resources Report of Investigations 34, 1 CD- Turner, A. K.; Schuster, R. L., editors, Landslides—Investigation ROM. and mitigation: National Academy Press; National Research Council Wegmann, Karl, 2004, Landslide inventory and slope stability mapping Transportation Research Board Special Report 247, p. 12-35. of urban growth areas in Cowlitz County: DGER News, v. 1, no. 2, Sidle, R. C.; Pearce, A. J.; O’Loughlin, C. L., 1985, Hillslope stability p. 2-3. [accessed Sep. 24, 2004 at http://www.dnr.wa.gov/geology/ and land use: American Geophysical Union Water Resources pubs/dgernews/] Monograph 11, 140 p. Wegmann, K. W.; Walsh, T. J., 2001, Landslide hazard mapping in Shannon & Wilson, Inc., 1965, Preliminary engineering studies of Cowlitz County—A progress report: Washington Geology, v. 29, landslide areas along proposed Interstate Highway 5, south Kelso, no. 1/2, p. 30-33. Washington: Shannon & Wilson, Inc. [under contract to] Washington Wells, R. E., 1981, Geologic map of the eastern Willapa Hills, State Highway Commission, 1 v. Cowlitz, Lewis, Pacific, and Wahkiakum Counties, Washington: Shannon & Wilson, Inc., 2000, Seattle landslide study: Shannon & U.S. Geological Survey Open-File Report 81-674, 1 sheet, scale Wilson, Inc. [under contract to] Seattle Public Utilities, 2 v. 1:62,500. Thorsen, G. W., 1989, Landslide provinces in Washington. In Galster, Western Regional Climate Center, 2005, Longview, Washington R. W., chairman, Engineering geology in Washington: Washington (454769)—Period of record monthly climate summary period of Division of Geology and Earth Resources Bulletin 78, v. I, p. 71- record, 1/1/1931 to 9/30/2005: Desert Research Institute Western 89. Regional Climate Center website. [accessed Mar. 10, 2006 at http:// www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?walvie] Turner, A. K.; Schuster, R. L., editors, 1996, Landslides—Investigation and mitigation: National Academy Press; National Research Wieczorek, G. F., 1996, Landslide triggering mechanisms. In Turner, Council Transportation Research Board Special Report 247, 673 p. A. K.; Schuster, R. L., editors, Landslides—Investigation and mitigation: National Academy Press; National Research Council Varnes, D. J., 1978, Slope movement types and processes. In Schuster, Transportation Research Board Special Report 247, p. 76-90. R. L.; Krizek, R. J., editors, Landslides—Analysis and control: National Academy of Sciences Transportation Research Board Wilkinson, W. D.; Lowry, W. D.; Baldwin, E. M., 1946, Geology of Special Report 176, p. 11-33. the St. Helens quadrangle, Oregon: Oregon Department of Geology and Mineral Industries Bulletin 31, 39 p., 1 plate. Walsh, T. J.; Korosec, M. A.; Phillips, W. M.; Logan, R. L.; Schasse, H. W., 1987, Geologic map of Washington—Southwest quadrant: Wills, C. J.; McCrink, T. P., 2002, Comparing landslide inventories— Washington Division of Geology and Earth Resources Geologic The map depends on the method: Environmental & Engineering Map GM-34, 2 sheets, scale 1:250,000, with 28 p. text. Geoscience, v. 8, no. 4, p. 279-293. Walsh, T. J.; Wegmann, K. W.; Pringle, P. T.; Palmer, S. P.; Norman, Wolfe, J. A., 1978, A paleobotanical interpretation of Tertiary climates D. K.; Polenz, Michael; Logan, R. L.; McKay, D. T., Jr.; Magsino, in the northern hemisphere: American Scientist, v. 66, no. 6, p. 694- S. L.; Schasse, H. W., 2002, Ground failures in the southern Puget 703. Sound lowlands caused by the Nisqually earthquake [abstract]: Geological Society of America Abstracts with Programs, v. 34, no. 5, p. A-112.

23 22 REPORT OF INVESTIGATIONS 35

Appendix. Bibliography of slope-stability investigations within the Cowlitz County urban corridor

The following citations are for geotechnical reports and geologic maps used in the creation of the landslide inventory presented in this report. Reference to specific citations is provided for individual landslides in the DATA_SOURC field within the database tables of the ESRI shapefiles ccuc_deep_seated_ landslides.shp and ccuc_shallow_landslides.shp. These reports are also referred to in the database table of the ESRI shapefile ccuc_report_boundary. shp. Some of the reports listed here are cited also in the main report text.

ADaPT Engineering, Inc., 2000, Slope assessment at Smith residence, Foundation Engineering, Inc., 1997a, Grim Road landslide A, additional 378 Vivian Road, Kalama, Washington: ADaPT Engineering, Inc. investigation, Kelso, Washington: Foundation Engineering, Inc. Project OR00-3706 [under contract to] Robert and Shirley Smith, Project 97200048 [under contract to] City of Kelso Public Works 3 p., 5 plates. Department, 1 v. Bednarz, S. L., 1999, The influence of geology on landslide mechanisms Foundation Engineering, Inc., 1997b, Kelso Reservoir geologic in southern Kelso, Washington: Portland State University, reconnaissance site map: Foundation Engineering, Inc. Project Environmental Geology G561 [unpublished report], 34 p., 1 plate. 95200071 [under contract to] City of Kelso, 1 plate [map only]. Cornforth Consultants, Inc., 1989, Engineering geologic reconnaissance, Foundation Engineering, Inc., 1998a, Highland Park Road landslide, Kelso property, Cowlitz County, Washington: Cornforth Consultants, phase 1 investigation, Kelso, Washington: Foundation Engineering, Inc. [under contract to] Kelso Associates I, 1 v. Inc. Project 97200066 [under contract to] City of Kelso Public David J. Newton Associates, Inc., 1996, Geologic field investigation Works Department, 5 p., 10 plates. and laboratory testing programs, proposed Carrolls Bluff project, Foundation Engineering, Inc., 1998b, Lower Grim Road landslide, Kelso, Washington: David J. Newton Associates, Inc. Project 652 phase 1 investigation, Kelso, Washington: Foundation Engineering, 102 [under contract to] Mr. Randall H. Bjur, 1 v. Inc. Project 97200065 [under contract to] City of Kelso, 7 p., 10 Evarts, R. C., 2001, Geologic map of the Silver Lake quadrangle, Cowlitz plates. County, Washington: U.S. Geological Survey Miscellaneous Field Foundation Engineering, Inc., 1999a, Fallert Bridge landslide, slope Studies Map MF-2371, 1 sheet, scale 1:24,000, with 37 p. text. treatment assessment, Cowlitz County, Washington: Foundation Evarts, R. C., 2002, Geologic map of the Deer Island quadrangle, Engineering Inc. Project 99200054 [under contract to] Cowlitz Columbia County, Oregon and Cowlitz County, Washington: U.S. County Department of Public Works, 10 p., 6 plates. Geological Survey Miscellaneous Field Studies Map MF-2392, Foundation Engineering, Inc., 1999b, Finn Hall Road realignment, 45 p., 1 plate, scale 1:24,000. geotechnical investigation, Cowlitz County, Washington: Evarts, R. C., 2004, Geologic map of the Woodland quadrangle, Clark Foundation Engineering, Inc. Project 99200018 [under contract to] and Cowlitz Counties, Washington: U.S. Geological Survey Cowlitz County Department of Public Works, 26 p. Scientific Investigations Map SIM-2827, 1 sheet, scale 1:24,000, Gene T. Strader Engineering, 1999, Geotechnical assessment of lot 2, with 38 p. text. off of Spencer Creek Road where Vivian Road intersects, Kalama, Fiksdal, A. J., 1973, Slope stability of the Longview–Kelso urban Washington: Gene T. Strader Engineering [under contract to] Gary area, Cowlitz County: Washington Division of Geology and Earth and Wendy Conradi, 3 p., 1 plate. Resources Open File Report 73-2, 4 p., 2 plates. Gene T. Strader Engineering, 2000a, Geotech assessment on lot 158 Foundation Engineering, Inc., 1993, Geotechnical investigation/slide Erion Lane, Woodland, Washington: Gene T. Strader Engineering repair, Fish Pond Road/Harlin slide, Cowlitz County, Washington: [under contract to] Thomas and Denelle Buck, 3 p., 7 plates. Foundation Engineering, Inc. Project P-611 [under contract to] Gene T. Strader Engineering, 2000b, Geotech assessment on lot 172 Cowlitz County Department of Public Works, 1 v. Erion Lane, Woodland, Washington: Gene T. Strader Engineering Foundation Engineering, Inc., 1995, Geotechnical investigation, Kelso [under contract to] Thomas and Denelle Buck, 3 p., 7 plates. Drive landslide A, Kelso, Washington: Foundation Engineering, GeoEngineers, Inc., 1996, Landslide and erosion hazards evaluation; Inc. [under contract to] City of Kelso, 1 v. Existing pipeline route—milepost 165 to 248, southwest Foundation Engineering, Inc., 1996a, Fallert Bridge landslide, proposed Washington: GeoEngineers [under contract to] Olympic Pipeline pump-out test and stability evaluation, Cowlitz County, Washington: Company, 1 v. Foundation Engineering, Inc. Project 96200006 [under contract to] GeoEngineers, Inc., 1998, Report—Geotechnical engineering services, Cowlitz County Department of Public Works, 3 p. slope failure evaluation, Aldercrest–Banyon Landslide, Kelso, Foundation Engineering, Inc., 1996b, Fallert Bridge landslide, Washington: GeoEngineers, Inc., [under contract to] City of Kelso, technical memorandum, Cowlitz County, Washington: Foundation 1 v. Engineering, Inc. Project 96200006 [under contract to] Cowlitz GeoEngineers, Inc., 1999a, Report—Geotechnical engineering services, County Department of Public Works, 4 p, 1 plate. slope stability evaluation, Haussler Road neighborhood, Kelso, Foundation Engineering, Inc., 1996c, Grim Road landslide geotechnical Washington: GeoEngineers, Inc. [under contract to] City of Kelso, services, Kelso, Washington: Foundation Engineering, Inc. 1 v. Project 96200018 [under contract to] City of Kelso Public Works GeoEngineers, Inc., 1999b, Report—Geotechnical engineering services, Department, 1 v. slope stability evaluation, Vista neighborhood, Kelso, Washington: GeoEngineers, Inc. [under contract to] City of Kelso, 1 v.

23 24 REPORT OF INVESTIGATIONS 35

GeoEngineers, Inc., 1999c, Supplemental geologic consultation, MC SQUARED, Inc., 1997, Review of various soils reports regarding Aldercrest–Banyon Landslide complex, Kelso, Washington: Three Rivers Estates: MC SQUARED, Inc. [under contract to] GeoEngineers, Inc. [under contract to] City of Kelso, 9 p. Three Rivers Estates Development, 4 p. GeoStandards, 2000a, Geologic reconnaissance report, proposed Myers, D. A., 1970, Availability of ground water in western Cowlitz Fish Pond/Kool Road subdivision, Carrolls, Cowlitz County, County, Washington: Washington Department of Ecology Water- Washington: GeoStandards Project L00-0186 [under contract to] Supply Bulletin 35, 63 p., 2 plates. Mr. Tim Duncan, 1 v. Neil H. Twelker & Associates, Inc., 1980, Fallert Bridge, Kalama River, GeoStandards, 2000b, Geotechnical evaluation, proposed Brighten Cowlitz County: Neil H. Twelker & Associates, Inc. [under contract Pl subdivision—upper three lots, Rose Valley, Cowlitz County, to] Arvid Grant and Associates, Inc., 4 p. Washington: GeoStandards Project L00-0188 [under contract to] PBS Environmental, 1997, Geotechnical investigation, Three Forks Mr. Tim Duncan, 1 v. development, Cowlitz County, Washington; PBS #12434.00: PBS GeoStandards, 2000c, Geotechnical evaluation, proposed Ross Road Environmental [under contract to] PET CAN Investments, 10 p., subdivision—lower two lots, Carrolls, Cowlitz County, Washington: 8 plates. GeoStandards Project L00-0187 [under contract to] Diversified Phillips, W. M., compiler, 1987a, Geologic map of the Mount St. Helens Equities, Inc., 1 v. quadrangle, Washington and Oregon: Washington Division of Gloyd, C. S.; Markich, G. T., 1981, Cowlitz County, Fallert Bridge, Geology and Earth Resources Open File Report 87-4, 59 p., 1 plate, L-9261, BROS-2008(3): Washington State Department of scale 1:100,000. Transportation intra-departmental communication to K. M Eggen Phillips, W. M., compiler, 1987b, Geologic map of the Vancouver and S. A. Moon, 2 p. quadrangle, Washington: Washington Division of Geology and Golder Associates, Inc., 1990, Geotechnical reconnaissance study of Earth Resources Open File Report 87-10, 27 p., 1 plate, scale proposed Park Ridge development: Golder Associates Inc. [under 1:100,000. contract to] City of Kelso Department of Public Works, 5 p., Roberts, A. E., 1958, Geology and coal resources of the Toledo–Castle 2 plates. Rock district, Cowlitz and Lewis Counties, Washington: U.S. Golder Associates, Inc., 2000, Geotechnical design recommendations Geological Survey Bulletin 1062, 71 p., 6 plates. for landslide hazard areas along the proposed fiber optic line, Shannon & Wilson, Inc., 1965, Preliminary engineering studies of collocated with the Williams gas pipelines—west alignment in landslide areas along proposed Interstate Highway 5, south Kelso, western Washington: Golder Associates Inc. [under contract to] Washington: Shannon & Wilson, Inc. [under contract to] Washington Williams Communications, 1 v. State Highway Commission, 1 v. Hart-Crowser & Associates, Inc., 1977, Interim report on slope Shannon & Wilson, Inc., 1998, Independent review of geotechnical movements, Fallert Bridge site on Kalama River, Cowlitz County, aspects of proposed Three Rivers Estates residential development, Washington: Hart Crowser & Associates, Inc. [under contract to] Kelso, Washington: Shannon & Wilson, Inc. [under contract to] Cowlitz County Engineering Department, 1 v. City of Kelso, 16 p., 5 plates. Howell, Michelle; Beckstrand, Darren; Flynn, A. G., 1999, Ground Sweet, Edwards and Associates, Inc., 1981, Fallert Bridge replacement, movement study, Haussler Road area, Kelso, Washington: Portland south footing test borings: Sweet, Edwards and Associates, Inc. State University, Environmental Geology G561 [unpublished [under contract to] Cowlitz County Department of Public Works, report], 24 p. [6 p.] J. B. Scott & Associates, 1997, Geotechnical evaluation of a parcel Washington State Highway Commission, 1972, C.S. 0802, SR-5, located in the SE 1/4 of the SE 1/4 of section 12 and the NE 1/4 of Longview Wye to Toutle River, L-1806, agreement no. Y-938, soils the NE 1/4 of section 13, T. 7 N., R. 2 W.W.M., Cowlitz County, and geology report: Washington State Highway Commission, 1 v. WA: J. B. Scott & Associates [under contract to] Groth & Company Washington State Highway Commission, 1973, SR-5 Longview Real Estate, Inc., 8 p. Wye I.C. VIC.—Brynion Street Grade Street undercrossing, sta. J. B. Scott & Associates, 1998, Response to the review of report titled, 171± to sta. 173±, Cowlitz County: Washington State Highways “Geotechnical evaluation of a parcel located in the SE 1/4 of SE Commission: 1 v. 1/4 of section 12 and NE 1/4 of NE 1/4 of section 13, T. 7 N., R. Washington State Highway Commission, 1977, Longview Wye to 2 W.W.M., Cowlitz County, WA” dated September 7, 1997 by the Brynion Street, Coweeman River Bridge: Washington State City of Kelso and Washington Department of Natural Resources: Highway Commission, 1 v. J. B. Scott & Associates [under contract to] Mr. David Groth, 8 p., 9 plates. Wells, R. E., 1981, Geologic map of the eastern Willapa Hills, Cowlitz, Lewis, Pacific, and Wahkiakum Counties, Washington: John McDonald Engineering, 1997, Preliminary soil investigation U.S. Geological Survey Open-File Report 81-674, 1 sheet, scale of phases I, II, and III of the Three Rivers Estates development; 1:62,500. Preliminary soil investigation for phases IV through IX of the Three Rivers Estates development: John McDonald Engineering [under Willamette Engineering & Earth Sciences, 1999, Geotechnical contract to] Randall H. Bjur, [62 p.] investigation Coweeman quarry, Kelso, Washington: Willamette Engineering & Earth Sciences, 1 v. Kleinfelder, Inc., 1996, Proposal for phase II hydrogeological investigation of the toe area of the Kalama River landslide, Yocum, B. J., 2001, Bypassing Harmony Drive: The Daily News, Dec. Cowlitz County, Washington: Kleinfelder, Inc. [under contract to] 2, 2001, Longview, Washington. n Foundation Engineering, Inc., 7 p. Livingston, V. E., Jr., 1966, Geology and mineral resources of the Kelso– Cathlamet area, Cowlitz and Wahkiakum Counties, Washington: Washington Division of Mines and Geology Bulletin 54, 110 p., 2 plates.