Piner Creek originates in the lower Mayacmas Mountains at Fountaingrove Lake. From its outlet at Fountaingrove Lake, Piner Creek flows down a relatively steep gradient, initially over a riprap lined channel, which has been modified in association with some alterations to lower Fountaingrove Lake. Thence Piner Creek flows northerly of an upscale modern office park before crossing under Redwood Highway and U.S. Highway 101. West of the U.S. 101 Freeway, Piner Creek winds through a retail and commercial/industrial area, before crossing under Piner Road near Coffey Lane; in this reach there is a large historic release to groundwater of solvent from manufacturing uses stemming back to the 1970s and 1980s.