impact of altering streambed gravels to reduce productivity of spawning habitats; additionally sedimentation of pools decreases the efficacy of anadromous fish summering habitat by increasing critical summer water temperatures in these pools. Pathogens appear to be linked to septic tank or leach field failures in some of the rural reaches, particularly in the upper valley sections. Nitrates enter the stream system from excess fertilizers applied to land uses in the drainage basin and may also be present in septic wastes improperly entering the creek. Sediment and nitrates may also enter the stream through urban stormwater runoff in the city of Sonoma reach. Wine production Because Sonoma Creek is the sole drainage flow of the Sonoma Valley Wine Country, it is a vital resource for aquifer recharge. Proportionally a greater percent of Sonoma Creek feeds recharge than its neighbors, the Napa and Petaluma Rivers. This outcome derives from the presence of pervious valley floor alluvial soils and the gentle stream gradients along the valley floor, where most of the reaches occur. The valley itself is part of the Franciscan Complex, which includes crumpled, uplifted terranes that have resulted from the subduction of the former oceanic Farallon Plate under the North American continent. The area is attended by volcanism and sediments, deposited in the lagoons behind its island arcs, which resulted from geological events dating from 140 to 42 million years. Recharge for the Sonoma Valley is critical because local rainfall is only about 29 inches (74 centimeters) per year. Grape growing and wine production require considerable groundwater extraction, and there is controversy over wineries use of annual creeks and waterways. Discharge to San Pablo Bay This large marsh area has been reduced considerably from its historic dimensions due to construction of multiple levee systems and encroachment by agriculture and other forms of development. This Napa-Sonoma Marsh has been formed largely by sedimentary deposits over the last two million years. The basement depositional layer is the Alameda group. Higher are Old bay mud and Young bay mud, between which there are intermediate deposits of the Alameda formation, which consists of alluvial and swamp origins. The entire marsh area is considered subject to liquefaction in the case of a major seismic event. The marsh is subject to diurnal tidal variations of approximately 5.5 feet (1.7 m). Historically the marsh supported an extremely diverse wetlands ecosystem, with a variety of primary productivity plants including