Topography Elevation is the most obvious feature distinguishing the Shawnee Hills from surrounding areas. As shown on the
Paducah; Kentucky: Illinois-Missouri-Indiana USGS map (1987) submitted with the petition, the Shawnee Hills range from higher in elevation than the glaciated land to the north and the river delta land to the south. Most of the highest elevations in Illinois, many above , are in the Shawnee Hills. Spectacular hills and ridges and a unique mesoclimate characterize the Shawnee Hills viticultural area. Nearly all vineyards in the Shawnee Hills viticultural area are on ridge tops and
bench lands ranging between in elevation. As such, the commercial vineyards in the Shawnee Hills area have experienced little or no spring frost or winter freeze injury. An additional benefit of the Shawnee Hills topography, the petition notes, is the enhanced air circulation caused by constant summer breezes, allowing faster drying of vineyard leaves and fruit clusters following rain, thus minimizing the risk of
fungal infections in an otherwise humid, wet climate. In contrast, the Mt. Vernon Hill County region immediately to the north of the Shawnee Hills was glaciated, and, as a result, is lower in elevation than the Shawnee Hills, according to the petition, which adds that the Mt. Vernon region is relatively flatter with no high ridges, cliffs, or
gorges. The topography of the Mt. Vernon Hill Country as "rolling farmland." Also in contrast, the Cairo Delta area south of the Shawnee Hills was flattened by water from both glacial melt and the tremendous flow and flooding of the two largest rivers in the country—the Mississippi and the Ohio, which eroded and replaced rock with
clay,
sand, and
gravel. According to the
Illinois State Geological Survey, the northern part of the delta area consists of Cretaceous, Gulfian McNary sand, and Tuscaloesa gravel. The southern part of the delta region consists of Paleocene and Eocene Wilcox Formation, Porters Creek clay thick. for
Mt. Vernon,
Anna, and
Cairo, Illinois. Anna is located within the Shawnee Hills viticultural area; Mt. Vernon, which is within the Mt. Vernon Hill Country region, is approximately north of Anna; while Cairo, which is within the Cairo Delta region, is approximately south of Anna. The petition compares Shawnee Hills, Mt. Vernon, and Cairo temperature data. It shows Shawnee Hills could be classified as a mid-Region IV climate in the Winkler heat summation climate classification system, with 3,770 growing degree-days. (During the growing season, one degree day accumulates for each degree Fahrenheit that a day's median temperature is above , which is the minimum temperature required for grapevine growth.
Soil While noting that soils vary in the Shawnee Hills region, the petitioners provided a general description contrasting the soils of the area with the soils of adjacent areas. As noted on the
General Soil Map of Illinois, prepared by J.B. Fehrenbacher (1982), the soils in the Shawnee Hills viticultural area are, generally, class XIII and class XIV, which tend to be thin
loess with or without residuum on limestone or interbedded sandstone, siltstone, and shale. The main soils are Alford, Hosmer, Wellston, and Zanesville. All of these soils are light colored, moderately developed, and moderately well drained. The western and southern parts of the area tend to have deeper soils, , on limestone. The central and northern parts of the area tend to have soil that is thick on sandstone, siltstone, and shale. The primary viticultural advantage of the soils within the Shawnee Hills is that they are moderately well drained and are of low fertility. Soil drainage in the Shawnee Hills area is moderate to excellent. In this area of
Karst topography, the loess soils, which tend to erode easily, are very good for quality
vines and
grapes. However, the best vineyard sites within the Shawnee Hills viticultural area are on flat ridge tops and
bench lands with deep soils that are not highly eroded. In contrast, the soil north of the Shawnee Hills in the
Mt. Vernon Hill Country are class II, which are primarily thick loess on Illinois drift. The main soils are Stoy, Weir, Bluford, Wynoose, Colp, and Del Rey. These soils tend to be much deeper than those in the Shawnee Hills, as well as more fertile but with poorer drainage. In general, these soils are more suited to growing such crops as
corn and
soybeans, which are the primary crops of the Mt. Vernon Hill Country, than to growing
apples,
peaches, and grapes, which are the primary crops in the Shawnee Hills area. The soils south of the Shawnee Hills in the
Cairo Delta, according to the petition, are primarily class XV, which are sandy to clay
alluvial sediments on
bottomlands. The soils include Lawson, Sawmill, Darwin, Haymond, Perrolia, and Karnak. These soils tend to be poorly developed and poorly drained. ==Viticulture==