To obtain official soil series description,
The Helena series consists of very
deep, moderately well drained, slowly permeable soils that formed in residuum
weathered from a mixture of felsic, intermediate, or mafic igneous or high-grade
metamorphic rocks, such as aplitic granite or granite gneiss that is cut by dykes
of gabbro and diorite, or mixed with hornblende schist or hornblende gneiss.
These soils are on broad ridges and toeslopes of the Piedmont uplands. Slope is
dominantly between 2 to 10 percent but ranges from 0 to 15 percent. Near the
type location, mean annual precipitation is 46 inches, and mean annual
temperature is 61 degrees F.
Taxonomic class: Fine, mixed, semiactive, thermic Aquic Hapludults
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