Les Cailloux means "the stones" and refers to the typical soil here which is composed of almost equal amounts of dirt and rocks. No agricultural product could grow in this soil except for grape vines and olive trees, which is why you often see grapes vines grown on land next to an olive grove. The grapes here are a blend of 80% Merlot and 20% Cabernet Franc. What is interesting is that Merlot grown here is different than Merlot grown anywhere else in the world. It's darker, richer, and more flavorful and adds the backbone to the wine that would usually be reserved for Cabernet Franc.
Bordeaux latitude makes it a marginal climate, which works better for Merlot than Cabernet. This is because Merlot ripens earlier, say by September 15th or 20th. Cabernet needs two to three more weeks on the vine to fully ripen. Those weeks are critical because it is also when the weather is at its most fickle. It's not unheard of for conditions like rain, which will water log the grapes or hail which will destroy them all together. Blending assures that the chateaux can still make a great wine. If the Cabernet makes it to ripeness, it goes into the blend. If it doesn't, then the blend is mostly Merlot. Think of it as the chateaux insurance policy.
When it all works out, we get a powerful yet majestic version of Bordeaux, at its best. The penetration of flavors from blackberry to cherry, mixed with earth and leather is all that's needed to tackle a prime rib with Yorkshire pudding.