downstream of Middlesbrough. The smaller River Esk flows from west to east at the northern foot of the North York Moors to reach the sea at Whitby. To the east of the Yorkshire Wolds the River Hull flows southwards to join the Humber Estuary at Kingston upon Hull. The western Pennines are drained by the River Ribble which flows westwards, eventually reaching the Irish Sea close to Lytham St Annes. Geography The countryside of Yorkshire has been called "God's Own County" by its inhabitants. Yorkshire includes the North York Moors and Yorkshire Dales National Parks, and part of the Peak District National Park. Nidderdale and the Howardian Hills are designated Areas of Outstanding Natural Beauty, as is the North Pennines (a part of which lies within the county). Spurn Point, Flamborough Head and the coastal North York Moors are designated Heritage Coast areas, and are noted for their scenic views with rugged cliffs such as the jet cliffs at Whitby, the limestone cliffs at Filey and the chalk cliffs at Flamborough Head. Moor House – Upper Teesdale, most of which is part of the former North Riding of Yorkshire, is one of England's largest national nature reserves. At High Force on the border with County Durham, the River Tees plunges over the Whin Sill (an intrusion of igneous rock). High Force is not, as is sometimes claimed, the highest waterfall in England (Hardraw Force in Wensleydale, also in Yorkshire, has a drop for example). However, High Force is unusual in being on a major river and carries a greater volume of water than any higher waterfall in England. The highest mountains in Yorkshire all lie in the Pennines on the western side of the county, with millstone grit and limestone forming the underlying geology and producing distinctive layered hills. The county top is the remote Mickle Fell (height above sea level) in the North Pennines southwest of Teesdale, which is also the highest point in the North Riding. The highest point in the West Riding is Whernside (height ) near to Ingleton in the Yorkshire Dales. Together with nearby Ingleborough (height ) and Pen-y-Ghent (height ), Whernside forms a trio of very prominent and popular summits (the Yorkshire Three Peaks) which can be climbed in a challenging single day's walk. The highest point in the Yorkshire part of the Peak District is Black Hill (height ) on the border with