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" in order to produce a large-scale map with cross sec- tions (Leighton, 1976). Map scales at this level vary from 1:1,000 to 1:10,000. Site-Specific Mapping Site-specific mapping is concerned with the identifica- tion, analysis, and solution of actual site-specific pro- blems. It is usually undertaken by private consultants for owners who propose site development and involves a detailed drilling program with downhole logging, sampling, and laboratory analysis in order to procure the necessary information for design and construction (Leighton, 1976). Map scales vary, but are usually not larger than I" = 50 '. Types of Maps The three types of landslide maps most useful to plan- ners and the general public are 1) landslide inventories, 2) landslide-susceptibility maps, and 3) landslide hazard maps. landslide inventories Inventories identify areas that appear to have failed by landslide processes, including debris flows and cut-and- fill failures. The level of detail of these maps ranges from simple reconnaissance inventories that only delineate broad areas where Iandsliding appears to Dave occurred (Figure 14) to complex inventories that depict and classify each landslide and show scarps, zones of depletion and accumulation, active versus inactive slides, -.- geological age, rate of movement, and other pertinent data on depth and kind of materials involved in sliding (U.S. Geological Survey, 1981; Brabb, 1984). Because simple inventories may be prepared mainly by interpreting aerial photographs, they can be put together in a short time at a relatively low cost. Simple inventories give an overview of the landslide hazard in an area and delineate areas where more detail- ed studies should be conducted. Detailed inventories provide a better understanding of the different landslide processes operating in an area and can be used to regulate or prevent development in landslide areas and to aid the design of remedial measures (U.S, Geological Survey, 1981). They also provide a good basis for the preparation of derivative maps such as slope stability, landslide hazard, and land use. landslide-susceptibility maps A landslide-susceptibility map goes beyond an inventory map and depicts areas that have the potential for Iand- sliding (Figure 15). These areas are determined by cor- relating some of the principal factors that contnbute to Iandsliding, such as steep slopes, weak geologic units that lose strength when saturated, and poorly drained rock or soil, with the past distribution of landslides. These maps indicate only the relative stability of slopes; they do not make absolute predictions (U.S. Geological Survey, 1981: Brabb, 1984). Landslide-susceptibility maps can be considered derivatives of landslide inventory maps because the in- EXPLANATION 1.~.I1 Areas inferred to be underlain by landslide deposits N o , 2 , MILES 4 , Figure 14. Detail from the landslide inventory map of the Durango 1. x 2. quadrangle, Colorado (Col- ton and others. 1975). 25