Pleistocene valley fills dominated by glaciolacustrine sediments commonly occur in southern British Columbia and northern Washington. The fills contain multiple glaciolacustrine units separated by glacial tills and outwash gravels reflecting multiple episodes of formation. Glacial overriding and landsliding during deposition have caused pre-sheared surfaces in present day valley slopes which show evidence of being at residual strength. We review the results of soil tests on samples from the Ashcroft and Grand Coulee dam areas. The geotechnics of these sediments is examined with an emphasis on the relationship between geotechnical index properties and residual strength parameters. The controls on residual strength are examined. Finally, the influence of varve thickness and pore water pressure are related to the effective stress condition of the slope. The precise characterization of residual strength is a key component of landslide hazard assessment of slopes developed in these materials.