IDL Procedure to read/write USGS DEMs

[John Brock <jbrock(at)cfcg.er.usgs.gov>]

I am working on integrating topographic data at various spatial
resolutions within a single
USGS 7.5 minute DEM.  This requires changing the data structure for a
DEM to
handle sections of variable resolution.

Does anyone know of an existing IDL procedure that reads or writes USGS
DEMs?
(DEM = digital elevation model).  If so, I would like to use it as a
starting point.

Thanks,

John Brock