Interestingly this is a 683 byte file (mighty small). It is a zip archive (maybe all kmz files are) -- when expanded (via unzip NGS_Topo_US_2D.kmz) I get a kml file. This is NGS_Topo_US_2D.kml and is 1834 bytes in size (still pretty small). This is an XML file and can be inspected with any ascii editor. The key line has the following URL reference:
http://services.arcgisonline.com/arcgis/rest/services/NGS_Topo_US_2D/MapServer/kml/regions/0-0-0.kmz?As of 12-2019, this is still online and available: So this is another project for me, and perhaps this thing can be revived. I should try it perhaps with my Windows copy of Google Earth. No time now. I had hoped this would just work.
Some other work on this general topic:
Adventures in Computing / tom@mmto.org