Oops.  Out spraying fungicide on beans, late to reply.

Here, I think the file extension for the DEM's and DTM's is .adf.  I am sure there are others.

When I load a DEM I get a grayscale image where the elevation value is represented by the range from black to white.  Then I create a polygon, clip the DEM, and use the contour tool to create contour lines.  But I am working with base county-wide datasets - they either take a long time to contour, or they crash my PC.