Editing Port wine (section)

===Wine regions===
[[File:Porto.Grahams03.jpg|thumb|Aging in wooden barrels]]

The demarcation of the Douro River Valley includes a broad swath of land of pre-[[Cambrian]] [[schist]] and [[granite]]. Beginning around the village of [[Barqueiros]] (about {{convert|70|km|abbr=on}} upstream from Porto), the valley extends eastward almost to the Spanish border. The region is protected from the influences of the Atlantic Ocean by the [[Serra do Marão]] mountains. The area is subdivided into three official zones: the Baixo (lower) Corgo, the Cima (higher) Corgo, and the Douro Superior.<ref name="ocw">{{Cite book |url=https://www.worldcat.org/oclc/70699042 |title=The Oxford companion to wine |date=2006 |publisher=Oxford University Press |editor-first=Jancis |editor-last=Robinson |isbn=0-19-860990-6 |edition=3rd |location=Oxford |oclc=70699042}}</ref>{{rp|536}}
* '''Baixo Corgo''' – The westernmost zone located downstream from the river [[Corgo River|Corgo]], centred on the municipality of [[Peso da Régua]]. This region is the wettest port production zone, receiving an annual average of {{convert|900|mm|in}} of precipitation and it has the coolest average temperature of the three zones. The grapes grown here are used mainly for the production of inexpensive ruby and tawny ports.<ref name="ocw"/>{{rp|536}}
* '''Cima Corgo''' – Located upstream from the Baixo Corgo, this region is centred on the town of Pinhão (municipality of [[Alijó]]). The summertime average temperature of the region is a few degrees higher, and annual rainfall is about {{convert|700|mm|in}}. The grapes grown in this zone are considered of higher quality, being used in bottlings of vintage, reserve, aged tawny, and late bottled vintage ports.<ref name="ocw"/>{{rp|536}}
* '''Douro Superior''' – The easternmost zone, extending almost to the Spanish border. This is the least cultivated region of Douro, due in part to the difficulties of navigating the river past the [[rapids]] of [[Valeira Dam|Cachão da Valeira]]. This is the driest and warmest region of the Douro. The overall terrain is relatively flat, with the potential for [[mechanical harvesting|mechanization]].<ref name="ocw"/>{{rp|536}}