The underlying rock is Cambrian Piperock, but the headlands are composed of different rock types, and structural influences are strong as in the other beaches of the Durness group. The western headland is composed of limestone, which is separated from the Piperock by a fault, while to the east lies Cambrian quartzites. Along the shore of the eastern part of the beach, however, there is a narrow outcrop of gneiss, which also occurs in a knoll backing the middle of the beach. Inland a depression bounded by steep margins occurs, with a veneer of glacial till of variable thickness. Offshore this till deposit seems to thin and become discontinuous, most of the ground except for the inner part of the bay being rocky or weedy. About two miles out, however, there is an extensive bank of sand parallel to the coast. The water offshore is shallow and gently shelving, with the underlying rock platform, cut mainly in limestone, appearing above water in the form of skerries and the fairly sizeable island of Eilean Hoan. These offshore skerries protect the beach area and neighbouring headlands from wave attack, and the fetch is very short except for a narrow sector to due north, and an equally narrow sector to the east-northeast.
Archaeology at Sangobeg
Salvage excavation was carried out on an archaeological site, discovered during the North Sutherland Coastal Zone Assessment Survey in 1998, in dunes at Sangobeg, near Durness in northern Sutherland. The excavation, conducted in 2000, uncovered the fragmentary remains of probable Norse-period settlement, including stone walling, a hearth and occupation deposits that had been truncated by erosion. Sealed beneath the Norse-period remains was the burial of a child of indeterminate sex, aged between 8–10 years, who had been placed in a flexed position on a bed of quartzite pebbles and covered with a mound of clean sand, capped with larger quartzite stones. The burial was dated by radiocarbon to 170 cal BC–cal AD 30 (GU-12535). For information about an archaeology find see Sangobeg Pict
Sangobeg Sands occupy a small embayment in the northwest to southeast trending coastline about two miles to the east of Durness. The beach is nearly 300 yards long and 150 yards wide, with a very narrow upper beach a few yards across. The nature of the terrain backing the beach restricts the blowing of sand inland, and maritime influences are confined to a very narrow zone. Pedestrian access is not particularly easy, since it is through croft land. The beach is thus little used for any recreational purpose although it is scenically attractive and a good view of it is obtained on driving eastwards along the road from Durness.
The relatively sheltered position of the beach behind the offshore skerries means that little marine erosion takes place. Some erosion occurs on both headlands however, but especially on the western limestone one.
Here there is evidence of attack by sea levels higher than that of today, in the form of caves, wave cut notches and abrasion platforms all standing above present high water mark. However these features grade into similar ones still evolving today, although the ledge vegetation on the limestone cliffs might suggest that retreat of the cliffs is slower than formerly. The limestone is close bedded, and dips very gently seawards, so that conditions are conducive to cliffing. On the eastern side of the headland, an entirely different type of rocky coast occurs on the gneiss, where the massive structure does not readily form cliffs and the profile to be convex and rounded. Neither of the headland areas or nearby sections of coast are likely to yield large quantities of sand for beach nourishment. The limestone will tend to dissolve rather than form sand, and the material eroded from the gneiss would tend to be large clastic fragments which would be in the cobble rather than sand calibre.
A second potential source of very limited quantities of sediment is the small stream which flows into the centre of the beach. The gneiss knoll behind the beach deflects one branch of the stream far to the west so that it flows through a marshy depression parallel to the beach and this marsh will act as a sediment trap and reduce the already small quantity of transported material. The other possible source of sand is from the offshore ground where glacial deposits have been laid down, and there is strong evidence to suggest that a large proportion of these deposits lying above wave base have already been swept onshore.
In terms of marine processes, the beach is relatively stable. Calculation of the c/p ratio is not possible, however, because the beach is convex seawards in plan, a repercussion of the influence of the offshore skerries. There is no marked tendency of the beach to re-orientate itself, although undercutting by storm waves of the machair front is most noticeable on the eastern part of the beach. This undercutting has exposed deposits of shingle under the blown sand, and it seems likely that this shingle, which is mainly of fairly angular quartzite fragments, is a raised beach. The shoreline of this raised beach is represented by a subdued cliff cut in till a short distance inland, and it is significant that the boulders with which the surface is strewn are completely lacking seawards of the till cliff. The shoreline was not levelled but is only a few feet above high water mark. Sand has blown inland over this raised shingle beach to give a very narrow zone of machair parallel to the shore. There is quite a steep reverse gradient of about 10° on the machair, which is little affected by erosion scars. Some marram colonisation is occurring at the eastern end of the beach where sand has accumulated against the undercut machair front, but otherwise the dune zone typical of the area found between the beach and machair (Figure 4) is lacking. The influence of blown sand on the vegetation is confined to the narrow machair fringe, and quickly dies out inland where the vegetation is typical of reverted croft land and moorland, although some bracken exists on the freely drained cliff cut in till backing the raised beach. Along the stream sides freshwater marsh communities occur, while on the limestone cliffs of the western headland a rich flora occupies the ledges. Croft land approaches close down to the beach and although most of the land is under a rather poor form of grazing it is not cultivated.
Grazing is fairly intensive, both by sheep and by rabbits which are numerous, and the sward is close cropped. Rabbit burrows are very numerous on the reverse gradient of the machair, but since there is shelter here from strong winds the burrows have not been enlarged into erosion scars.