When applied to wine, the French word terroir indicates both the terrain and the entire micro- and macro-environments in which grapes grow and ripen. Terroir therefore comprises soil, precipitation, sun, wind, exposure and all other natural influences. It expresses continuity of character in a region's wines from year to year. It is the basis for regional personality and a source of reference when judging quality.
Not all wine growing areas concentrate on the unique qualities of their environment. But the smaller the region and the more specific its parameters, the more recognizable its identity. As confirmed by its AVA status, the Spring Mountain District is one area whose terroir distinguishes it from other northern California vineyards and the rest of the Napa Valley.
The climate of Spring Mountain is generally classified as Region IV, with some of the cooler years being a Region III and the warmer ones being a Region V. As compared to the Napa Valley floor, the region has a more moderate temperature range during the growing season—cooler days and warmer nights—as a result of the typical daily cycle.
Mornings warm more quickly here than on the valley floor (most Spring Mountain vineyards lie above the fog line), while afternoons are cooled earlier by maritime winds from the Pacific. These unusual afternoon breezes direct from the ocean—over the mountain rather than up the valley from San Pablo Bay—do not occur as often in other areas on the eastern slopes of the Mayacamas and are at times unique to Spring Mountain. Spring Mountain also receives 10-15 inches more annual rainfall than the Napa Valley floor or the eastern slopes of the valley. Total precipitation can range as high as 70 to 95 inches in some of the wettest years.
Overall, the climate produces an unusually long growing season—with bud break in mid-March, veraison about July 1, and harvest from mid-September to November.
Soil depths vary but tend to be deeper than in nearby mountain terrain. The region contains mostly residual upland soils with only a few areas of alluvial soils at the lower elevations. The soils are derived almost equally from Franciscan sedimentary rocks (sandstone and conglomerates) and Sonoma volcanic formations. This equal mix distinguishes the region from adjacent mountain areas. To the north, in the Diamond Mountain area, soils are almost entirely of volcanic origin. To the south, in the Mount Veeder area, soils are primarily sedimentary.
For an in-depth review of Spring Mountain terroir, read "Spring Mountain Terroir" by Paul Skinner, PhD., Terra Spase, Inc.
Noted Napa Valley terroir author and viticultural consultant Paul Skinner has worked with many Spring Mountain District vineyards and wineries over the past decade, and is the viticulture and terroir authority on Spring Mountain terroir.