Topography Upper Lake Valley was selected as the name for the appellation to reflect its topography that encompasses a series of valleys, along with their surrounding hillsides, that run in a north-northeasterly direction from the shores of Clear Lake. The northern boundary is generally concurrent with the northern boundary of the established Clear Lake AVA and separates the AVA from the higher, rugged elevations of the Mendocino National Forest. The eastern boundary follows the elevation contour and also separates the AVA from the Mendocino National Forest. The southern boundary follows the northern shore of Clear Lake. A portion of the western boundary follows a series of roads and the elevation contour to separate the AVA from the higher terrain of the
Mayacamas Mountains. The remainder of the western boundary is a straight line between points that is concurrent with the established Clear Lake AVA boundary and also separates the AVA from the Mayacamas Mountains. The distinguishing features of the Upper Lake Valley are its
geology and
hydrogeology, soils, and climate. Annual predicted rainfall amounts within the Upper Lake Groundwater Basin, where the AVA is located, range from , which provides sufficient hydration for grapevines. To the east, west and south of the AVA, annual predicted rainfall amounts are lower, while in the region to the north, the annual predicted rainfall is approximately . The AVA has a median of 202 frost-free days per year. The median, minimum, and maximum frost-free periods within the AVA are substantially shorter than those of the established AVAs to the east, southeast, and west. The median and maximum frost-free periods in the AVA are longer than their counterparts in most AVAs to the south of the AVA, with the exception of the established Red Hills Lake County AVA. The number of frost-free days in the region to the north of the AVA was not available. Late frosts can damage new vine growth and early frosts can impact the ability of grapes to reach a desirable sugar level. The median GDD accumulation in the Upper Lake Valley AVA is 3,158, while the maximum is 3,434 and the minimum is 2,809. According to the petition, GDD accumulations within the AVA are suitable for growing a variety of grapes, including Sauvignon Blanc. The median GDD accumulation for the AVA is substantially smaller than those of established AVAs to the east, southeast, south, and west. The maximum GDD accumulation in the AVA is less than the maximum GDD accumulation in each of these established AVAs, with the exception of Benmore Valley AVA to the west and Big Valley District–Lake County AVA to the south. The minimum GDD accumulation in the AVA is lower than those of established AVAs to the east, southeast, south, and west. GDD data was not provided for the region to the north of the AVA. Within the AVA, wind speeds between account for 82.88 percent of the daytime wind speeds and 88.86 percent of nighttime wind speeds. Winds with speeds below, defined as "calm," occurred only 2.23 percent of the time during daytime hours and 3.04 percent of the time during nighttime hours. Wind speeds greater than were not recorded within the AVA. The petition states that constant, gentle winds keep grapes and leaf canopies cool and dry, and reduce the risk of mildew. According to the petition, a larger percentage of wind speeds in three established AVAs to the southeast and south of the AVA are less than , and in two of these AVAs, winds with speeds exceeding were recorded. Wind speed data was not available for the regions to the north and west of the AVA. The petition also requested the expansion of the Clear Lake AVA boundary so that the entire Upper Lake Valley would be contained within it. The petition noted that the expansion area, located in the northern portion of Scotts Valley along
Scotts Creek, has elevations within the range of those found elsewhere in the Clear Lake AVA where its vineyards are elevated between . For comparison, the expansion petition notes that the vineyard within the expansion area sits at . The expansion petition also included a map of the Clear Lake watershed, which was described as having an important effect on the climate of the Clear Lake AVA. The expansion petition notes that the map includes all of Scotts Valley, including the expansion area, in the Clear Lake watershed. Finally, the climate of the Clear Lake AVA places it in Winkler Regions II and III. The expansion petition notes that annual GDD accumulations in the expansion area range from , which also places the expansion area in Winkler Regions II and III.
Soils According to the petition, soils from three general soil map units make up over 56 percent of the total area of the Upper Lake Valley AVA: Millsholm–Skyhigh-Bressa; Still–Lupoyoma; and Tulelake–Fluvaquentic–Haplawuolls. Millsholm–Skyhigh–Bressa soils are formed from
sandstone and
shale and are primarily
loams and
clay loams. They are moderately deep, moderately-well to well-drained, and have slopes that range from moderately sloping to steep. These soils are shallower than soils in the other two map units. They may still be suitable for viticulture, however, since the petition states the quality of fruit is better, although yields are usually lower, on soils limited in depth by
hardpan, rock or clay
substrata. Soils from the Still–Lupoyoma general map unit occur on the nearly-level valley floors and consist of very deep, moderately-well to well-drained loams and
silt loams. According to the petition, most vineyards in the AVA are planted on these soils due to their gentle slopes, which create less of an
erosion hazard and provide good drainage. These soils are also deep, which allows roots to extend further. Soils from the Tulelake–Fluvaquentic–Haplawuolls map unit are very deep, poorly drained silty clay loams that occur in marshy and reclaimed areas around Clear Lake and
Tule Lake. The petition states these soils can be suitable for viticulture if the poor drainage can be mitigated. To the north of the Upper Lake Valley AVA, the soils belong to the Maymen–Etsel and the Sanhedrin–Speaker–Kekawaka soil map units. These shallow soils contain
outcroppings of large stones and are not very prevalent in the AVA. To the east of the AVA, the most common soil map units are the Maymen–Etsel, Sobrante–Guenoc–Hambright, and the Sanhedrin–Speake–Kekawaka units, which are also not common within the AVA and occur mostly on very steep slopes. South of the AVA, within the Big Valley District AVA, the soils belong to the Cole-Clear Lake Variant-Clear Lake general soil map unit. To the west of the AVA, the soils are from the Millsholm–Skyhigh–Bressa soil map unit and then transition to the Maymen–Etsel soil map unit in the higher elevations of the Mayacamas Mountains. == References ==