In which southwest French region are Tannat, Cab Franc, and Cab Sav primarily used to produce red wines?

The region in southwest France where Tannat, Cabernet Franc, and Cabernet Sauvignon are primarily used to produce red wines is Madiran. This region is particularly known for its robust and tannic red wines, with Tannat being the dominant variety. Tannat is celebrated for its deep color, high tannin content, and aging potential, which makes it well-suited for creating structured and complex red wines.

In Madiran, the typical blend often includes a significant proportion of Tannat, complemented by other varieties like Cabernet Franc and Cabernet Sauvignon, which contribute to the wine's overall flavor profile and complexity. The terroir of Madiran, with its clay and limestone soils, coupled with a climate that allows for warm grapes, influences these varieties to thrive, resulting in wines that are rich and full-bodied.

This combines to make Madiran distinctively recognized for these grape varieties, setting it apart from the other regions listed, where those specific varietals may not be as prominent or characteristic to the wine's identity.