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Soil and litter movement on steeper slopes is obvious when significant accumulations of soil and litter material have moved downslope as a • result of siol mantle disturbance from grazing animal trampling. How- ever, on level or gentle slopes, trampling may result in "churning" the soil to dust or mud. This churning changes the soil structure and contributes to subsequent soil displacement during wind or rainstorms. Soil movement usually becomes more obvious as slope steepness in- creases and occurs most readily when antecedent soil moisture is very low or very high. However, two items may be necessary to minimize soil erosion: (1) a ground cover of at least 70 percent (as shown in Fig. 7) and, (2) a soil bulk density of 0.70 or less (Packer, 1961). Evidence of soil displacement takes two forms on sloping rangeland. (1) With excessive trailing by livestock or wildlife, the surface is imprinted with nearly level terraces. The banks between these terraces ate often steep, exposing soil to subsequent downward movement by water and gravity. The terrace may become a water- course during rain and serves to concentrate runoff into a water flow with erosive force. (2) Trampling displacement, not concentrated in trails but more generally distributed over the slope, is marked by soil accumula- tions on the uphill side of perennial plants and by mounds or ridges downslope. Such displacement is less easily observed than terrace trails but probably is more serious. Terrace trails • suggest a degree of stability, possibly only temporary, in which the surface has been reformed over time to accommodate an animal concentration. In contrast, general trampling displacement over the slope suggests that there is no stability except where soil may accumulate on the uphill side of a fairly permanent obstruc- tion. Lichen lines or breaks, are indicators of soil movement. These lines appear if the surface soil has eroded around stones and rocks covered with lichen. Since lichen only grows on the aboveground portion of stones and rocks, there will be an abrupt, horizontal, break between lichens and rock area that originally was below soil surface (Fig.B). Lichen growth will keep pace with normal geologic erosion and possibly slightly accelerated erosion. Pronounced lichen lines on stones and rocks are reliable evidence of soil movement at a moderate to severe rate. The space between the lichen lines and the present soil surface indicates the amount of soil movement that has occurred. Lichen lines are more obvious on elevated terrain, i.e., ridges and mesas. They may not appear on lower slope areas where soil losses may be replaced by deposition of soil or litter that has moved from farther upslope. Caution: Frost heaving of stones and rocks may create lichen lines, giving a false soil loss appearance. u 29