Soil Type: Andisols

Andisols are soils that have formed in volcanic ash. They differ from those of other orders in that they typically are dominated by glass and short-range-order colloidal weathering products such as allophane, imogolite, and ferrihydrite. Globally, Andisols are the least extensive soil order and only account for ~1% of the ice-free land area. They occupy ~1.7% of the US land area, including some very productive forests in the Pacific Northwest region. Below is a map of andisols eight suborder's distribution in the U.S.

I have also included a link to an article below which is about infiltration rate in andisols and the effect of changes in vegetation cover.

http://www.jswconline.org/content/61/3/153.abstract