I am using QGIS 2.0. I have downloaded USGS 1:100,000 topographic maps which show adjacent areas. The topographic maps were digitized with the borders (I've seen them called "collars", I think) as part of the rasters. When I load the vertically (north-south) adjacent rasters, the border areas of course overlap the map areas of each other. I have tried to convert one raster to a vector so that I could use the vectorized map as a mask to crop the other raster, but it didn't work. (My computer just kept spinning -- sort of froze up.) I have not found, here or elsewhere, discussions of using one raster to crop or clip another.
If I can use one raster map to crop another, adjacent-but-overlapping raster map, then how can I do it?