A model is proposed for predicting the spatial variation in colluvial soil depth, the results of which are used in a separate model to examine the effects of root strength and vertically varying saturated conductivity on slope stability. The soil depth model solves for the mass balance between soil production from underlying bedrock and the divergence of diffusive soil transport. This model is applied using high-resolution digital elevation data of a well-studied site in northern California and the evolving soil depth is solved using a finite difference model under varying initial conditions. The field data support an exponential decline of soil production with increasing soil depth and a diffusivity of about 50cm2/ yr. The predicted pattern of thick and thin colluvium corresponds well with field observations. Soil thickness on ridges rapidly obtain an equilibrium depth, which suggests that detailed field observations relating soil depth to local topographic curvature could further test this model. Bedrock emerges where the curvature causes divergent transport to exceed the soil production rate, hence the spatial pattern of bedrock outcrops places constraints on the production law.The infinite slope stability model uses the predicted soil depth to estimate the effects of root cohesion and vertically varying saturated conductivity. Low cohesion soils overlying low conductivity bedrock are shown to be least stable. The model may be most useful in analyses of slope instability associated with vegetation changes from either land use or climate change, although practical applications may be limited by the need to assign values to several spatially varying parameters. Although both the soil depth and slope stability models offer local mechanistic predictions that can be applied to large areas, representation of the finest scale valleys in the digital terrain model significantly influences local model predictions. This argues for preserving fine-scale topographic detail and using relatively fine grid sizes even in analyses of large catchments.

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The two Chinese maps recently discovered in a Han tomb of the second century B.C. antedate by 1,300 years the two maps which were previously the earliest extant in China; elsewhere in the world they are predated only by the Babylonian clay tablets. These Han maps which are of high quality in terms of scale consistency, information content, and use of symbols are much more advanced than the Babylonian tablets. The two maps, one topographic and one military, portray effectively the terrain, roads, settlements, and military operations of an area in and around southern Hu-nan Province. All features on the maps are depicted with welldesigned abstract symbols, and the military map is colored. These maps provide evidence of a much higher level of cartographic achievement in ancient China than had previously been realized.INCE the 1950s the People's Republic of S China has undertaken intense archaeological investigations which have unearthed large quantities of artifacts, manuscripts, and human remains. In 1973, three maps of the second century B.C. were discovered in a tomb from the Han Dynasty, in the city of Chang-sha in Hu-nan Province. These maps, drawn on silk, antedate by 1,300 years the two Hsi-an maps carved in stone, which were previously the earliest extant.* More important than the early date, however, is the extraordinary quality of these maps in scale consistency, information content, and use of symbols.The Chinese have restored and reported on two of the maps, one topographic and the other military. The published reports deal with the restoration procedures, map content and accuracy, and the history of the mapped area.'