Some people believe that the soldiers from this fort were abandoned by the Spanish and left to fend for themselves. One theory is that the intermarried with the Indians and became part of what is now called the Melungeon community in the southern Appalachians. I've written a long summary of what I've read about the Melungeons. It is at
The Melungeons: Appalachian Mystery. Those with an interest in little known history should check it out.
WFTR
Bill