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Stable (S)
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Stable slopes generally rise less than 15 percent in grade, except in local areas of low groundwater concentration or competent bedrock. Stable slopes include rolling uplands and lowlands underlain by stable material such as unweathered till and/or peat deposits which, although inherently weak, have no significant slope.
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Intermediate (I)
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Intermediate slopes are generally steeper than 15 percent except where conditions such as weaker material and/or abundant groundwater exist. Identified areas include slopes of sand and gravel, till, or thin soils over bedrock which have no known failures.
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Unstable (U)
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Unstable slopes are considered unstable because of geology, groundwater, slope and/or erosional factors. They include areas of landslides and talus too small or obscure to be individually mapped.
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Unstable Recent Landslide (Urs)
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Identifies recent or historically active landslide areas. [Note
that Urs designation is based on investigations carried out in the late
1970s; subsequent landsliding is not reflected on these maps].
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Unstable Old Landslide (Uos)
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Identifies post-glacial but prehistoric landslide areas.
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Modified (M)
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Modified slopes are highly modified by human activity and include areas of significant excavation or filling. Slope response to a combination of natural processes and human activities may be unpredictable.
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