Figure 4.--A, Plasticity chart showing the plotted locations of samples AT-1 and AT-3 from the active portion of the Slumgullion landslide. Symbols identify types of materials that typically plot in the respective areas of the graph as follows: CL, inorganic clays of low to medium plasticity; ML or OL, inorganic silts and very fine sands with very low plasticity and organic silts and silt-clay mixtures of low plasticity; CH, inorganic clays of high plasticity; and OH or MH, organic silts and clays of medium to high plasticity and inorganic silts. Soils with a high content of active clay minerals, such as montmorillonite, typically plot well above the A-line (see fig. 4B). B, Location of common clay minerals and Slumgullion landslide samples AT-1 and AT-3 on Casagrande=s plasticity chart (adapted from Holtz and Kovacs, 1981).