The commune covers an area of . The eastern (and smaller) part of its territory lies within the fertile, central plain or "depresión intermedia", (Chilean Central Valley) but the extense western part is hilly and somewhat drier, a typical "Cordillera de la Costa" terrain, which requires supplemental irrigation to support its varied cultivations.
This area lends itself nicely to wine growing and cereal cultivation. Therefore, San Javier has some of the better vineyards and quality wines of the bountiful Maule Valley, in the Chile's central valley viticultural regions or appellations.