I am trying to mosaic multiple DEM grids into one DEM mosaic. I am using a file geodatabase created in ArcCatalog 10, and creating a new Mosaic Dataset within it. Then I am adding the rasters, which are DEM data from the United States at 10 meters. I included pyramiding and calculating statistics from the advanced settings (though it never seems to actually successfully calculate statistics). The rasters are successfully added, but when I view the mosaic in the preview tab of ArcCatalog or in ArcMap only the Boundary and Footprints are visible. The Images are not showing up. I have tried different settings and used some DEM files from other parts of the country, but they all yield the same results. I eventually realized that the DEM's were were the source of the problem. The vendor who made the images needed to crop the images, but instead essentially made all values beyond certain parameters null. So the footprint doesn't match the size of the image and it is throwing everything thing off. I'm wondering if there is any way to deal with this discrepancy within ArcGIS.