Still in use ~ critical phrase. There's another structure in East Central Ohio that is probably several decades older ~ looks like a sacrasty ~ first part of a church you might build out in the wilderness before you had any parishners. You can go on the net and in moments match up the style with that of standard Spanish frontier stuctures ~ all the way back!
They owned the Ohio Valley for a good long while ~ a couple of centuries before the French tried to move in! They did things ~ long forgotten things. (SEE: Old Stone Fort ~ http://www.midwesternepigraphic.org/croghan.html )
All of these old churches must have been built by deists. ;-)
The Old Stone Fort reminds me of churches (oratories, actually) that dot Ireland, particularly in the west.
I would love to know the orientation of the building as that might provide a clue as to its intended use.
(I find the name Isleta to be curious as well.)
Thanks for sharing!