I am trying to perform a sedimentation analysis for a watershed. I have created multiple rasters that I need to multiply together. When I multiply the four rasters together with the raster calculator I have negative and positive values. However, the lowest value in the rasters being multiplied is zero. I can multiply up to three of them together without this happening but all four seems to add negative values. I am using ArcGIS 9.3.1 and all rasters have the same projection, cell size, and are in a GRID format. Any ideas as to why negative values are showing up?