<P> From all of the district of Llanes the view to the south is dominated by the limestone mountain wall, which rises steeply to 744 m at L'Abá . The ridge forming the wall shields the view of the higher Sierra del Cuera above, of which the highest point (in Llanes) is La Peña Blanca, 1177 m . Between the two ridges there are hidden valleys, draining into cave systems . The largest of these valleys is La Llosa de Viango . Unlike the heights of the Picos de Europa further to the south, these valleys are green and pastoral . The mountains are part of the Cordillera Cantábrica, which runs across most of the north and northwest of Spain . </P> <P> From September 6, 1937 to September 22, 1937, 5,000 men of the Republican forces held off over 33,000 Nationalists, in this area, in an epic resistance which became known as the Battle of El Mazuco . </P> <P> The district contains numerous caves, including a site of archaeological interest at Nueva, and the Cueva Bolado (43 ° 24 ′ 04" N 4 ° 45 ′ 51" W ﻿ / ﻿ 43.40111 ° N 4.76417 ° W ﻿ / 43.40111; - 4.76417) near La Pereda which also contains ancient art as well as open passages . </P> <P> There are also several significant' wild' cave systems, including </P>

Where does the last name llanes come from