The Sierra Foothills rise slowly from the Central Valley to the west, with a noticeable change in vegetation at 1,000-feet (305 m) elevation; thus, this is where the region begins, transitioning from grasslands to chaparral and woodlands. To the east, the elevation tops out at 4,000-feet (1,220 m), considered the limit for viticulture here. The Foothills are on the lower western slope of the Sierra Nevada, noted in the AVA petition as consisting of a large block of granitic rock overlain with volcanics and older metamorphic rocks.
Mountains/River/other key influences
The terrain of the Sierra Foothills becomes more rugged from west to east, especially as the elevation rises. A diversity of terrain in general makes for a variety of microclimates and differences in slope, aspect and elevation. The entire AVA is within the San Joaquin-Sacramento River watershed. The Yuba River travels along the north boundary of Nevada County.
The soils of Nevada County and the larger Sierra Foothills region are formed from metamorphic, granitic and volcanic parent material, considered residual soils, with a large diversity of specific soil types.
The climate is marked by dry summers and relatively warm winters, resulting in grapes with higher acid and later ripening times. In the petition for the Sierra Foothills AVA it was noted that the climate of warm, sunny fog-free days, moderated by Delta breezes and cool nighttime breezes from the Sierras, make it an ideal growing and maturing climate for premium wine grapes. Rainfall is limited to winter, but tends to be more significant (15 to 40 inches/38-102 cm) than in the Central Valley below (6 to 20 inches/15-51 cm). The higher the elevation, the greater the difference between daytime highs and nighttime lows.