The physicists at Los Alamos sometimes had trouble interfacing with local government, and so a new small county was carved for them out of Sandoval County. But a small bit was left over, so now Sandoval has an exclave of about 3 km2 between Los Alamos and Santa Fe counties. I found a map [old link removed] that shows the fragment, and also the reason for its existence: it is part of San Ildefonso Indian Reservation. (The rest of the Reservation is in Santa Fe County; and the map also suggests that the eastern part of the new county was taken from Santa Fe.)
Later: Another map (click Topo and zoom in).
hi anton
your map links here seem to have zoned out
so if i can add this still other & later one
http://www.mytopo.com/maps.cfm?search_string=ildefonso%2C+nm
& my best wishes for you or anyone else properly celebrating this rare dual tripoint exclave
both tricorners of which appear to be marked & easily accessible
ak md
ps
there exist only the common nontripointed sort of exclaves & the rare double tripointed ones such as this
& nary a single single tripointed exclave in all creation
it seems
A landlocked exclave with a single tripoint is impossible.