I am trying to import a vegetation data raster in Esri GRID format from the USDA into QGIS. One file ("w0001.adf") can be added using "add raster", but the attribute table and other info register as error or errors. Using the "ArcInfo/Binary directory" does not work either.
The .adf file is one component of an Esri GRID 'file', much like the .shp is one component of a shapefile. The other component files generally aren't or don't need to be accessed individually. If you can load that w0001.adf file and see the raster image, I suspect you're seeing all the data. I opened/added the file in Arc with no issue. In looking at the attribute table for the raster there, there's just a second, coded, numeric value field - you won't see the text strings describing what those coded values are (that info is listed in the metadata).
The data opens with no issue in QGIS 2.8.1. The raster contains only the coded values 1-6. These coded values are described in the metadata:
Six values of ownership:
1 = Federal (Public): Owned by the federal government. FIA Codes 11-13, 21-25.
2 = State (Public): Owned by a state government. FIA Code 31.
3 = Local (Public): Owned by a local government. FIA Code 32.
4 = Family (Private): Owned by families, individuals, trusts, estates, family partnerships, and other unincorporated groups of individuals that own forest land. FIA Code 45.
5 = Corporate (Private): Owned by corporations. FIA Code 41.
6 = Other Private (Private): Owned by conservation and natural resource organizations, unincorporated partnerships and associations, and Native American tribes. FIA Codes 42-44.
There are no other attributes, which means there is no information about what State a cell is in. To extract forest ownership type for each state, you will have to get a US States dataset and use that to analyse the forest ownership data. You should ask a separate question for that.