As it follows, we shall describe how the Metroplitan region´s three orographic (study of the geographical reliefs) units develop.
– Coastal ranges: is the natural boundary with the region of Valparaiso, characterized for emerging strongly and seeming a wall southwards the Aconcagua river (at the northern part of the region). It has heights near the 2.000 meters, obstructing communications between Santiago and the coast, such as the mountain ranges of the Roble hills (2.222 masl), La Campana (1.828 masl), Vizcachas (2.046 masl), the Toble Alto (2.185 masl) and the heights of Chicauma and Lipangue.
In front of Santiago, the Coastal ranges decrease and only exceptionally reaches 1.000 masl (with the highlands which flank the Maipo river). Farther south it recovers height forming deep valleys.
– Intermediate depression: also called the Santiago basin, occupies a fertile valley between the Chacabuco mountain ranges, northwards, and the Paine Narrows, by the south. It has a length of 80 km southbound and 35 km wide westbound. This basin has been refilled mainly by material coming from the erosion of the Andes Ranges and by volcanic ashes and it is occupied by the urban area of Santiago city (at a height of 520 masl) but there are some outstanding isolated hills, such as Santa Lucia, the Blanco and the Chena.
– Andes Ranges: it presents itself massif and high, with snowdrifts crowning some heights. It also has an important volcanic activity which coincides with some of its greatest heights: Tupungatito or Bravard (5.682 masl), San José (5.856 masl) and Maipo (5.264 masl) volcanoes. From these has come the material (volcanic ashes and the product of fluvial and glacial erosion) that filled the Andean valleys and the intermediate depression. Other important ranges heights are the following mountains: Tupungato (6.570masl), Marmolejo (6.108 masl), Nevados del Plomo (6.050 masl9 and the Piuquenes (6.017 masl).
