Piner Creek is a stream in northeast Santa Rosa, California, United States (38°27′40″N122°45′05″W) which originates as an outlet of Fountaingrove Lake. Piner Creek discharges to Santa Rosa Creek which in turn joins the Laguna de Santa Rosa. The upper reaches in the foothills of the Mayacamas Mountains are at elevations of 200 to 300 feet (60 to 90 meters), while the lower and middle reaches are located on the Santa Rosa Plain at elevations of between the 110- and 140-foot (33- and 43-meter) contours; therefore, these lower reaches have a gradient of about 1:250 toward the southwest. Geologic studies in the lower and middle reaches of Piner Creek indicate groundwater levels ranging from three to 15 feet (one to 5 meters) below the surface.