My own thinking (and imagination) has been stimulated by the ideas and suggestions of others; so pardon me if the following is out of my depth.
I'm wondering about the possibility that TC is the Creator of the Land as an embodiment of his unrealized hopes and dreams for his marriage to Joan. His white gold wedding ring is the "Arch of Time" within which the Land is located. That would explain how and why TC is the white gold, and why his ring (and not just anyone else's) would have the power and significance it does in the Land. It would also explain why Joan's white gold wedding ring also has the power and significance that it does. Such a connection between TC, his wedding ring and his marriage, and the Land would also fit the similarities and connections between the condition of the Land and Joan's condition.
Linden Avery is first brought into the Land, along with TC, when she attempts to intervene in the efforts of TC on Joan's behalf; eventually, she replaces Joan in TC's affections, etc. TC even gives his ring to Linden. I'm wondering if the final fate of the Land doesn't hinge on a final severing of TC's attachment and commitment to Joan. That relationship remains to some extent unresolved, although it is troubled and tenuous, and Joan's distress over her abandonment of TC is (literally) chipping away at the Land and its stability. Perhaps, if the wholeness that TC yet needs to discover and achieve (what he has yet to learn) will involve the ending of his ties with Joan and a completion of his new "marriage" to Linden; at which point the Land, as such (or as it has been), would come to an end (or be reborn as something altogether new and different, such as the embodiment of now-realized hopes and dreams in a marriage to Linden).
Perhaps Jeremiah, Linden's son, becomes a building block (or a builder) of a new Land, created by a new relationship between TC and Linden

Like I said, just thinking out loud here. If I haven't lost everybody, and if I'm not completely insane in these rambling thoughts, maybe some of the rest of you might care to comment in response. . . .

Thanks, at any rate, for giving it some thought.