This is NS4275 : Dumbowie Hill - the south-eastern summit
. This flat summit area is slightly hollow; a fact that, before excavations took place here, led to the surmise that it was an extinct volcano, with the summit forming the crater. In fact, the hill, which is composed of igneous rock, is indeed a volcanic plug, but the reason for the slightly raised rim of the summit is that the turf conceals a circular wall, which is 9 to 10 metres in diameter, and which is formed of flat sandstone slabs.
This wall enclosed an Iron Age fort. Its entrance was on the western side, and is apparent in this photograph as a dip in the line of the edge of the summit, near the left-hand edge of the picture; in this view, the shadows produced by the low sun make the dip more apparent. Aside from the circular wall itself, there are two terraces on the western side of the hill, which may be traces of additional enclosing ramparts (see the link in the previous paragraph for a view of these).
The summit area (see NS4275 : Dumbuie Dun
and NS4275 : Dumbuie Dun
for views from different angles) was excavated by the Helensburgh Naturalist and Antiquarian Society in 1895; see NS4275 : Dumbuie Dun
. A reproduction of a painting of the dun as it appeared during excavation, with the wall fully exposed, can be found in the journal "Proceedings of the Society of Antiquaries of Scotland", Volume 30 (1895-96), pages 291 to 308. It is unfortunate that the bulk of the report is devoted to certain objects that were found during excavation; they were the subject of much controversy at the time, and they are now known to be fakes that were planted on the site while the dig was in progress (the culprit was never identified). A few years later (1898), the same Helensburgh society excavated at NS4173 : Dumbuck Crannog
, and similar fake antiquities were found.