The Spanish Missions of Georgia were all burned to the ground by English pirates centuries ago. Even the knowledge of the whereabouts of the sites of these once thriving Catholic communities is, for the most part, lost. The indigenous people the missions served (like the Apalachee, the Timucua, the Guale, and others) were wiped out by the English, and with them, the memory of their customs and heritage. The low country woodlands have reclaimed these sites, but there had been dozens of Spanish missions along the coast of what is today Georgia, and in some cases, these missions were already a century or more old when the Spanish missionaries began to establish their missions on the west coast of California.
Because the living memory and sites are lost in history, we are left to speculate to some extent about how the missions might have looked. Archaeologists help us now and then when they find the sites and study them. The Catholic Church is also good at keeping lists and records that help us piece things together. We also have other Franciscan missions in similar places that did survive that help us complete the picture.