Flanking both sides of Route 128 connecting Sonoma’s Alexander Valley with Mendocino's Anderson Valley are the vineyards that comprise the Yorkville Highlands appellation. In 1998 the region was approved as an AVA, primarily because of its distinctive soils and temperatures relative to surrounding growing areas. Yorkville Highlands' rocky soils, with high-gravel content, differ from the loamy, clay soils common to neighboring appellations. These highly-porous soils allow for superior water drainage, forcing the roots of vines to dig deep for water. The result is low-vigor vines that yield concentrated fruit. Daytime temperatures here fall between those of hot Alexander Valley and cool Anderson Valley. However, at night Yorkville Highlands experiences greater cooling than either of these adjacent appellations. The moderate temperatures of the AVA are suitable for Sauvignon Blanc, and also show great promise for reds like Cabernet Sauvignon and Merlot.