While the Apple II version of GEOS was never as popular or well-supported as the Commodore variant, there are still a few within the A2 community who enjoy this early GUI.  Oliver Schmidt has taken the time to dig a little deeper into GEOS, and having discovered the secrets of the file structure, published his findings over at cc65.org.  Says Schmidt:

Although the Apple GEOS filesystem is based on ProDOS 8 the Apple GEOS files are not standard ProDOS 8 files. I’m not refering to file content here but to the file structure – meaning that Apple GEOS files aren’t seedling, sapling nor tree files.

You can read more details about the fruits of his efforts in his announcement in this comp.sys.apple2 thread.  The findings themselves are available to read here.