The solum ranges from medium acid through mildly alkaline. The mean annual soil temperature is 38 degrees F., and the mean summer soil temperature is 46 degrees F., with an 0 horizon 4 inches thick. These are the Chris , Nutras and Seitz series. These soils lack fragmental IIC horizons at depths of less than 50 inches. Also, Chris soils have coarse fragments mainly less than 10 inches in diameter and Seitz soils have hue of 7.5YR or yellower in the B2t horizon.
Vulcan soils are on gently to steeply sloping mesa tops and sides.
Slope gradients range from 2 to 30 or more percent. The soils formed in very stony parent materials weathered from highly fractured rhyolite or similar bedrock. At the type location the average annual precipitation is 20 inches with peak periods of precipitation occurring during the spring and summer. These are the competing Nutras soils and the Ruby soils. Ruby soils have mollic epipedons and lack A2 horizons.