Introducing Halo Ranch: Part of a resilient future for San Francisco Estuary

The San Francisco Estuary is one of the world’s truly unique tidal marsh systems. It’s also one of the most endangered, compromised by habitat loss from past development and threatened by the risk of future sea level rise.

California is fortunate to have strong and committed visions for restoring the marsh. Those efforts have given RES clear targets in siting, designing, and constructing the Halo Ranch complex, a unique site in the Petaluma River Baylands, just southeast of the City of Petaluma.

Halo Ranch is both a wetlands mitigation bank and an adjoining custom turnkey mitigation opportunity for protecting threatened tidal marsh species. The site occupies a unique position in San Pablo Bay, and RES’ restoration plan checks many boxes that leverage that unique location to accomplish state and regional goals for marsh restoration:

• It aligns with the State Water Resources Control Board requirements for siting mitigation banks in accordance with watershed plans.
• It is a priority area identified by, and following the restoration guidelines of, the US Fish and Wildlife Service’s Recovery Plan for Tidal Marsh Ecosystems of Northern and Central California.
• The restoration plan RES developed in coordination with the Interagency Review Team reflects a deep historical study and restoration principles informed by the San Francisco Estuary Institute’s Petaluma Valley Historical Hydrology and Ecology Study.
• Sea level rise and flooding models predict the site is not prone to complete inundation and can help form refugial high-tide habitat for the wildlife corridor. RES is re-establishing the wetland and tidal marsh areas accordingly.

Halo Ranch

Halo Ranch is situated in a priority restoration area. The US Fish & Wildlife Service's tidal marsh recovery plan for the region* urges “prompt implementation of tidal restoration projects” and identifies three critical targets, including “Petaluma baylands on both sides of the river and towards the mouth, with opportunities for expanding habitat around rare species populations and restoring gradual gradients from high marsh well into uplands.” Photo credit: Google Earth. *Recovery Plan for Tidal Marsh Ecosystems of Northern and Central California, US Fish and Wildlife Service, 2013.

The Restoration of Halo Ranch

The restoration of Halo Ranch is a textbook example* of using historical ecological studies to inform the design. Historically, the dark green areas were wet meadow, and the light green were tidal marsh and sloughs. Restoring tidal marsh and seasonal wetlands at the Bank (blue outline), where they historically existed, will create diverse habitats that can extend through the Turnkey site (pink) to connect to the Petaluma Marsh across the river. *Petaluma Valley: Historical Hydrology and Ecology Study, March 2018, San Francisco Estuary Institute-Aquatic Science Center.

Halo Ranch Prior to Restoration

Halo Ranch Mitigation Bank, prior to the beginning of the restoration, following a long period of agricultural use.

Designing in Accordance with Watershed Plans

RES designed this restoration to follow the State Water Resources Control Board's requirements for siting mitigation banks in accordance with watershed plans. Restoring this mix of seasonally wet meadow, tidal marsh, stream, and riparian areas also meets the USFWS goals for creating “substantial areas of wide diversity of tidal marsh and associated habitats.”

Petaluma Marsh

The Petaluma Marsh, which abuts the Halo Ranch Turnkey Mitigation Site opportunity, is the largest remaining natural tidal brackish marsh in California. It is established habitat for the California Ridgeway’s rail (yellow) and the salt marsh harvest mouse (purple). Halo Ranch can extend that habitat in accordance with the USFWS recovery plan for the area: “Habitat connectivity will increase the potential for population and genetic exchange, especially for less mobile species such as the salt marsh harvest mouse. If fringing marshes are used to establish connectivity, they should be as deep (from shore to bay) as possible from inboard to outboard edge, and should have wide and well vegetated high tide refugial habitat, capable of accommodating sea level rise.

Bay Area Sea Level Rise Analysis

As the USFWS plan calls out “opportunities to restore upland ecotones and accommodate upper extremes of sea level rise exist … around the Petaluma Marsh.” The location of Halo Ranch, at the interface with rising terrain to the northeast, put it into a strong position to create habitats resilient to even the worst-case sea level rises. This map from the Bay Conservation and Development Commission Adapting to Rising Tides study shows that Halo Ranch can accommodate worse case scenarios for sea level rise while still containing upland transitional habitats.

Credit Release

The first release of credits is expected in late 2023 for Halo Ranch Mitigation Bank, covering wetlands, stream and riparian mitigation needs. It is the only bank in the northern region of the San Francisco Bay estuary area that will offer these credits. Site tours are available for both the Halo Ranch Mitigation Bank and the Halo Ranch permittee-responsible mitigation (PRM) turnkey opportunity, which contains habitat for the salt marsh harvest mouse and California’s Ridgway’s rail. Photo credit: Drone image by California State Lands Commission

Historically, Halo Ranch was a complex of seasonally wet meadows, streams, and riparian habitats situated just upslope of the Petaluma River. The seasonally wet meadows and riparian areas transitioned to a tidal marsh abutting the Petaluma River. Over time, farmlands replaced the wetlands and riparian habitat, while levee construction severed the hydrological connection to the Petaluma River and San Francisco Estuary.

Conservation efforts created a foothold in the adjoining land west of the river – the Petaluma Marsh preserve. This became a key factor in the site selection criteria for Halo Ranch. Re-establishing the seasonally wet meadow, stream, riparian habitat, tidal marsh, and sloughs and connecting them to tidal marsh habitat already under protection expands the wildlife corridor in an optimal way.

The restoration of Halo Ranch will help create the conditions for a continuous, thriving wildlife habitat supporting recovery plans for the salt marsh harvest mouse, Ridgway’s rail, salmonids, longfin smelt, and other denizens of the unique San Francisco Estuary.