Río Biobío
The valley runs an un-interrupted length of 360 km from Angostura de Pelequén in the north to Bío Bío River (37°40' S) in the south. It broadens from 12 km at Molina (35°05' S) in the north to 74 km in the south at Laja (37°15' S) the relief being gently undulating. Conglomerate of Andean provenance cover large swathes of the Central Valley being less common to the west near the Coast Range. Occasionally the valley contains isolated hills and mountains made up of basement rocks. At the latitudes of Temuco the Coast Range is subdued to such degree the Central Valley coalesces with the coastal plains.