Much of the western coastline of the islands is machair, a fertile low-lying dune pastureland. Lewis is comparatively flat, and largely consists of treeless moors of blanket peat. The highest eminence is Mealisval at in the south west. Most of Harris is mountainous, with large areas of exposed rock and Clisham, the archipelago's only Corbett, reaches in height. North and South Uist and Benbecula (sometimes collectively referred to as The Uists) have sandy beaches and wide cultivated areas of machair to the west and virtually uninhabited mountainous areas to the east. The highest peak here is Beinn Mhòr at . The Uists and their immediate outliers have a combined area of . This includes the Uists themselves and the islands linked to them by causeways and bridges. Barra is in extent and has a rugged interior, surrounded by machair and extensive beaches.