The Rocks District of Milton–Freewater Viticultural Area (The Rocks AVA) is a sub-appellation of the Walla Walla Valley AVA, which itself is a sub-appellation of the Columbia Valley AVA.It is named for a unique alluvial fan resulting in rocky soils with "baseball sized" basalt cobbles covering the earth, and is notable as being "the only AVA in the United States whose boundaries are defined by the soil type".