The upper reach of Piner Creek watershed is characterized by presence of Goulding cobbly clay loam soil; this soil has slopes of up to 15 percent and is subject to moderate erosive potential. The actual soil depth is typically only about and may contain up to 25 percent cobblestones. Historic use of this soil has been for grazing. As the stream approaches the Santa Rosa Plain immediately east of U.S Highway 101, slopes diminish to a gradient of five to 15 percent and the predominant soil type is Felta very gravelly loam. This Felta soil is characterized by an upper surface grayish-brown color and texture of a fine, sticky and plastic nature.