Flash forward to just now. In coincident conversation with drummerdude, he mentioned the Ozark Iron Works and sent me some link that I glanced over, and noticed that the description on this historic places registry application directly matched that of the temples. We had stumbled into the furnaces of the iron works, which operated in the mid 1870's. These were by far the bitchinest furnace stack I'd ever seen.
Check it:
Furnaces as we approach from the tracks

From the front:

Looking in through the main archway on the east side

Standing inside the main archway, showing keystone and a precariously placed block of sandstone.

Looking up through the smoke stack

View of top of structure

Also about 200 feet east of the furnaces were the ruins of a brick building, which served as the iron works store, eventually burning in 1968.

Around back

Pretty cool stuff. Many thanks to drummerdude for the registry link, found here