Chalk Hill is a tiny, evocatively named AVA in northern Sonoma, nestled among the eastern hills of the famous Russian River Valley.
As the AVA title implies, Chalk Hill's soils are the factor that sets it apart from the rest of the Russian River Valley – especially the soil make-up known as Franciscan Assemblage. Named after the San Francisco area (where it was first analysed and classified), Franciscan Assemblage is a chaotically distributed mix of greywacke sandstones, limestones, deep-sea radiolarian cherts, altered mafic volcanic rocks (greenstones), serpentinites, shales and high-pressure metamorphic rocks. It is the chert and limestone component in particular that justifies the name Chalk Hill.
© Sonoma County Vintners
In addition to the Franciscan Assemblage, there are Goldridge Series soils. Highly characteristic of Sonoma Valley, these consist of deep, moderately well-drained soils based on material weathered from weakly consolidated sandstone. Chalk Hill's vignerons are proud of their unusual terroir, and no doubt grateful for the talking point and marketing 'edge' it provides.
Many millions of years ago, the area that roughly equates to the modern-day Russian River Valley was a shallow inland sea, perhaps not dissimilar from the San Francisco, San Pablo and Grizzly bays of today. After a prolonged period of seismic and volcanic activity, the valley took on its current form (although, as confirmed by the area's susceptibility to earthquakes, the tectonic activity is far from over). The net result was (more or less) the current topography of the Alexander Valley, with Chalk Hill consisting of the very southern end. To the west is a low-lying coastal range, while to the east are the Mayacamas, which separate Napa from Sonoma.
The higher elevation of the Chalk Hill AVA brings with it warmer temperatures, which suit the Cabernet Sauvignon, Merlot and Sangiovese vines grown on the sunny hillsides. On the lower slopes towards the Russian river, mostly white grapes are planted. These include Chardonnay, Sauvignon Blanc, Semillon and Pinot Grigio.
The better-known wineries based here are Rodney Strong Vineyards (the first winery to label a wine with the Chalk Hill AVA title), Lancaster Estate, J Vineyards and Chalk Hill Estate.