I have eight DEM tiles that I downloaded from the USGS National Elevation Dataset. The individual rasters are displaying correctly, but when I try to combine them in a Raster Mosaic I get arbitrary values (3.4+038 -> -3.4+038), which is considered to be NoData.
I've tried several times, half the time I get a warning message upon creation of the Mosaic (001003: Datum Conflict) even though I was sure to match coordinate systems. I've even imported the coordinate system from one of the rasters going into the mosaic.
The mosaic shows the footprint of the DEM, but none of the data
I had a similar problem here, but I followed the process of converting to tif before I tried to mosaic the images.