Mountains and hills of England the Pennines (often called "the backbone of England") continues into the Yorkshire Dales, a limestone-dominated area of broad valleys and moorland. The Yorkshire Three Peaks are some of the highest summits in the area, which became a national park in 1954. The Yorkshire Dales end at Skipton, and a short distance to the south is a range of moors that rises up between the urban cores of Greater Manchester and West Yorkshire. The range has no continuous name - the western part as far as Blackburn is called the West Pennine Moors, the eastern part north of the A646 (including
Clark Mountain Range on the "sky island" which occasional rains create above 6,000 feet (1,800 m). The north side of the crest contains a small forest of white fir trees, which is extremely difficult to reach. Clark Mountain is one of three mountain areas where these rare trees persist; Kingston and New York Mountains are the other two areas where the Rocky Mountain white fir – "Abies concolor" can be found in California. Interstate 15 traverses the mountain pass between the Clark Range and the Mescal Range to the south. The small town of Mountain Pass is located just south of the range