I'm using 10m DEM rasters from the NRCS Data Gateway for a large portion of California. The problem is some strange tiling that appears after merging, but isn't present in the original data (before merging). The grids create low points, so flow accumulation etc is drawn into them.
I've tried mosaic to new raster, create raster catalog and filter in ArcGIS 10.2, merge and build vrt in Qgis2.4 but the problem persists throughout.
The grids represent flat lows in the curvature raster on the merged edges of the DEM rasters. Note that those lines are the edges of BOTH of the mosaiced DEM, creating 2 lines.
The lines are flat lows, which creates a problem trying to do any sort of slope stability or hydrologic analysis...which is the whole point of this exercise.
Unmosaiced DEM Rasters: 
Curvature raster generated from Mosaiced raster using bilinear interpolation: 
EDIT: The data and mosaic method were the problems: The data itself has edge effects built in and I was using nearest neighbor instead of bilinear interpolation
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