Courtesy of Josh Collins, Ph.D., San Francisco Estuary Institute (SFEI)

D. Petaluma River Wildlife Area

D1. Physiographic Features
The Petaluma River Wildlife Area (PRWA) consists of a variety of discontinuous parcels of tidal marshlands of different ages and physiography along the western side of the Petaluma River. The largest parcel is the Petaluma Marsh, which comprises the most northern extent of the proposed NERR. Petaluma Marsh is the largest and least disturbed example of ancient tidal marshland in California. It includes the only examples of undisturbed high-order tidal marsh drainage systems that were historically typical of tidal marshland in much of the region. These drainage systems are complexly dendritic, and include pronounced natural levees along the largest channels, extensive slump blocks on the large- and medium-sized channels, and large, natural, tidal marsh ponds on drainage divides. Petaluma Marsh is bordered on the west by San Antonio Creek, which drains a privately-owned rural watershed used for cattle gazing, and Neils Island, which is a hilltop surrounded by existing and diked tidal marshlands.

The remaining parcels of the PRWA consist of youthful, low-to-medium elevation tidal marshlands, and diked-historical tidal marshlands that are either isolated from the tides, or subject to muted tidal action. Most of the tidal marshlands along the immediate margin of the Petaluma River, downstream of Petaluma Marsh, have evolved natural through then adjustment of the river to decreased tidal prism. As the neighboring tidal marshland were reclaimed, the tidal prism of the river decreased, and the river channel shoaled and became more narrow, through sediment accretion. Along the river edge, accretion has produced linear mudflats and tidal marshlands, with parallel drainage systems that lack tidal marsh ponds. Two, small exceptions are diked parcels that have recently been restored to tidal action. In these parcels, tidal marshland is forming with abundant small channels in dendritic arrays. The diked-historical marshlands are characterized by differential subsidence that has produced a complex mosaic of shallow depressions, which are locally referred to a seasonal wetlands.

The PRWA represents the almost whole estuarine gradient of the Petaluma River. Average salinity decreases with distance upstream. The upper reaches of the Petaluma Marsh along the river and along San Antonio Creek are brackish, whereas the marshlands at the mouth of the river are saline.

D2. Climate
The climate of the PRWA is strongly influenced by the Petaluma Gap, which is a long stretch of very low elevations of the California Coast Range Mountains between the outer coast and Petaluma Valley. Marine influences, including on shore winds and summertime fog, move through the Petaluma Gap and extend down the Petaluma River toward San Pablo Bay. These influences moderate temperatures throughout the Petaluma Valleys. Because the PRWA is north of the southern extent of the Mid-pacific High Pressure Zone, and almost due east of the Petaluma Gap, it is commonly in the track of major north pacific storms. The area is therefore subject to occasional intense rainfall, and large amounts of seasonal runoff.

D3. Hydrology
The parcels of mature tidal marshland are located above the Mean High Water datum, and are therefore not inundated by every high tide. Some of the tidal marsh ponds on drainage divides are subject to desiccation during autumn, when evaporation rates are greatest and the high tides are lowest. The youthful, tidal marshlands along the river downstream of Petaluma Marsh are most at, or below, Mean High Tide, and are therefore inundated by almost every high tide. As stated above, these areas do not have tidal marsh ponds.

The hydroperiod of the seasonal wetlands of the diked historical tidal marshlands is controlled by rainfall, drainage ditches, and tide gates. The management of the surface waters is inexact, such that the monthly distribution and abundance of surface water varies from year to year.

The Petaluma River and San Antonio Creek are the only perennial streams that enter directly into the PRWA. Both Streams are gaged, and a flood-warning system is maintained for the Petaluma River by the city of Petaluma. Local overland sheetflow and intermittent runoff from hills that adjoin the west side of the site in some places create minor salinity gradients between the base of the hills and the tidal marshlands. Runoff may be a significant contribution to the seasonal hydrology of the diked marshlands that are completely isolated from the tides.

D4. Geology
The bedrock of the hills that partly border the PRWA is the Franciscan Melange, which is a complex assemblage of small and large rock types, dominated by silt stones and shales, and separated by zones of seismically sheered and crushed materials. Hard rock components can include sandstone, greenstone, chert, serpentine, and glaucophane shists. No serpentine is known to occur within this site, however.

Two major, active fault traces are associated with the PRWA. Both are right-lateral slip faults that trend north-south. The Burdell Fault exists just west of the Petaluma River. The Rogers Creek Fault apparently extends beneath the Petaluma Marsh from its northwest edge, north of the town of Lakeville. Paleo-ecological studies at Petaluma Marsh suggest tectonic uplift of the west side of the Petaluma Valley, but no evidence has been found for major seismic effects on the marshlands (Byrne, personal communication).

D5. Biological Resources
The tidal marshlands of the PRWA support two species (California Clapper Rail ands the Salt Marsh Harvest Mouse) that are listed as endangered by both the federal and the California State species protection laws. The Petaluma Marsh is part of the northern limits of the California Clapper Rail. Its distribution within the Petaluma Marsh extends upstream with increasing aqueous salinity during drought years. The site also supports a variety of other species of special status or concern, including the Black Rail, Golden Eagle, Prairie Falcon, Northern Harrier, Black-shouldered Kite, Short-eared Owl, Salt Marsh Song Sparrow, and Soft Bird’s-beak.

The hills that are nearby some parcels support oak savanna and oak woodlands. San Antonio Creek supports a continuous corridor of riparian trees that extends from the upper reaches of the watershed to the tidal marshlands. This is one of the few of such riparian connections remaining in the region.

The flora of the tidal marshlands is typical of youthful low-elevation, and mature high-elevation salt or brackish marshlands of the region. The high marsh plain is dominated by pickleweed. The natural levees of the largest channels of the mature marshland typically support gumplant, yarrow, frankenia, coyote brush, and fathen, in addition to pickleweed. The lower intertidal areas of channels within the more saline reaches of the PRWA support Pacific cordgrass. Further upstream, where conditions are more brackish, the lower intertidal areas support tules, often in a narrow zone slightly higher in tidal elevation than Pacific cordgrass.

There are no published reports on the species composition of the fish fauna of these tidal marshlands. However, a pilot project to sample fishes of tidal marsh channels has recently been initiated at Petaluma Marsh. Early results indicate that these tidal marsh channels support the endangered tidewater Goby, in addition to juveniles of some other species more typical of San Pablo Bay (Heib, personal communication). based upon otter trawls and midwater trawls, the most common fish species in San Pablo bay are northern anchovy, Longfin smelt, Jacksmelt, Pacific herring, striped bass, American shad, starry flounder, shiner perch, and Yellowfin Goby (Herbold et al. 1992).

D6. Historical Development and Site Use
In general, the human history of the PRWA is typical of tidal marshlands in the northern reaches of the San Francisco Estuary. The Coastal Miwok were the native peoples in the vicinity of Petaluma Marsh and other places further downstream and west of the Petaluma River. Olempali was a large Coastal Miwok town at the base of Mount Burdell, just west of Petaluma Marsh. Other, smaller habitations existed along the river. There is evidence that these peoples hunted waterfowl, fished, and harvested shellfish in the tidal marshlands. During the mission period that preceded California statehood, the lands west of the river were part of a large Mexican land grant. Ever sense that period, most of the surrounding lands have been used for cattle gazing and dairy operations. Remnants of an early adobe building exist at Olempali. The adobe, other buildings dating back to the Victorian age, and some of the surrounding oak woodlands were recently dedicated as Olempali State Park. Soon after statehood, much of the tidal marshlands that bordered the river began to be reclaimed, mainly for oat hay production.

The Petaluma River has played a very important role in the amount and kind of land use along the river. Warehouses and landings were constructed in the late 1800’s at Lakeville, which was on the crossroads of stage routes between Petaluma, Sonoma, and points south along the River; Donahue Landing, on the east side of the river upstream of its confluence with San Antonio Creek; and at the headwaters of Black John Slough, which extends westward from the river further downstream. Until the advent of the railroad, the river served as the primary commercial corridor for the transport of bulk goods and materials between the Petaluma Valley and other parts of the Bay Area.

Commercial and recreational waterfowl hunting was popular in the tidal marshlands of the river before the turn of the century. Recreational hunting was supported by blinds constructed beside the larger tidal marsh ponds. Responsibility for these blinds and hunting “rights” have been unofficially transferred among generations of hunters. many of the ponds have historical names.

D7. Present Site Uses
The PRWA is mainly used by the public for fishing, waterfowl hunting, and passive recreation. A moderate amount of recreational boating occurs along the river. The adjoining diked tidal marshlands and hills are used for cattle grazing and oat hay production. Petaluma Marsh is the site of a number of ongoing, university-based research projects of regional importance, focusing on tidal marsh evolution and the ecological effects of sea level rise. The research is based at the Davis and Berkeley campuses of the University of California.

D8. Zoning and Surrounding Land Uses
Almost all the lands surrounding he PRWA are zoned for agriculture. A small portion of the parcels near the mouth of the Petaluma River is bordered by lands zoned for residential uses.

D9. Dredging
The Petaluma River is important for commercial navigation and is maintained by regular dredging, within the PRWA. For 1996, the projected volume of dredged material is 300,000 cy (SFBCDC and COE, 1995). It is interesting to note that the tidal prism of Petaluma Marsh that is exchanged with the river via San Antonio Creek is sufficient to prevent any need for the creek to be dredged. The marina at the confluence of the Petaluma River and San Antonio Creek is the only marina in the Bay Area that accepts deep-draft sailing vessels and does not require dredging.

D10. Pollution Sources
Major potential pollution sources for the PRWA include the outfall of the sewage treatment facility for the city of Petaluma, leaching from an active sanitary landfill near the confluence of the Petaluma River and San Antonio Creek, runoff from grazed lands, and the tides. None of these sources have been quantified for the PRWA parcels upstream of San Pablo Bay. The Regional Monitoring Program for trace substances occupied a water sampling station at the mouth of Petaluma River. The monitoring results from this station indicate that the tidal water exceeds the EPA standard for human consumption for copper, mercury, nickel, and for a variety of trace organic compounds, including total PCB’s.

D11. Infrastructure
The PRWA has a rural setting with a variety of widely distributed infrastructure. The major roadways for access to the PCR are US 101, CA 37, and Lakeville Highway. Public marinas with boat launches and docks exist at Black Point, Mira Vista, Lakeville, and the city of Petaluma. A small cinder block building exists in the middle of Petaluma Marsh, where a radio tower once stood. The dirt road that was constructed to service the tower still extends from Neils Island to the generator building. The electrical lines that served the radio tower have not been maintained. Petaluma Marsh contains numerous small landings that are used by waterfowl hunters. The diked parcels of the PRWA include perimeter levees and passive water control structures. At this time, there is no primary staging area or center of attraction at the PRWA. However, the county of Marin has initiated a recreational use plan for par of the western side of the Petaluma River.