I downloaded a selected sub-set of the USGS National Elevation Data (NED) using their online GUI. This download came in the form of three files.
The names of the files are
To load the rasters, I have found I go into these files and load the file of type ".adf". (Is this not true?)
It works just fine for one file at a time. When I load all three in turn, the QGIS layers list shows three little raster icons with tiny "previews" of the area covered; the name of each one happens to be identical to the other two (w001001).
They always load "flat" -- that is, one gray-scale tone. So I use the Properties dialog to stretch to MinMax. When I do, only one of the three will change and show the range of shadings indicative of elevation range. The other two turn black.
How can I get all three to show the MinMax range?