Almost all the southern boundary with Inverness-shire consists of a rampart of peaks, many of them Munros:  To the north of Glen Torridon are the masses of Liathach (), Beinn Eighe (), Beinn Alligin () and Beinn Dearg (). On the northeastern shore of Loch Maree rises Slioch (), while the Fannich group contains six Munros, the highest being Sgurr Mor (). The immense isolated bulk of Ben Wyvis (), forms the most noteworthy feature in the north-east, and An Teallach () in the north-west appears equally conspicuous, though less solitary. Only a small fraction of the west and south of the area is under in height. Easter Ross and the peninsula of the Black Isle are comparatively level. The longest stream of the mainland portion of Ross and Cromarty is the River Orrin, which rises from the slopes of An Sidhean () and pursues a north-easterly course to its confluence with the River Conon after a run of about , a small part of which forms the boundary with Inverness-shire. At Aultgowrie the stream rushes through a narrow gorge where the drop is considerable enough to make the Falls of Orrin. The River Blackwater flows from mountains in Strathvaich southeast for until it joins the Conon, forming soon after it leaves Loch Garve the small but picturesque Falls of Rogie. Within a short distance of its exit from Loch Luichart the Conon pours over a series of cascades and rapids and then pursues a winding course of , mainly eastward to the head of the Cromarty Firth. Situated above Glen Elchaig in the southwest of the region are the Falls of Glomach. The stream giving rise to them drains a series of small lochs on the northern flanks of Beinn Fhada (Ben Attow) and, in an almost unbroken sheet over a metre in width, effects a sheer drop of 110 m, and soon afterwards ends its course in Glen Elchaig. The falls are usually visited from Invershiel 11 km to the south-west. 12 miles south-east of Ullapool, on the estate of Braemore, are the Falls of Measach, formed by the Droma, a headstream of the River Broom. The cascades, three in number, are close to Corrieshalloch Gorge. The River Oykel, throughout its course, forms the boundary with Sutherland.