This project will fund preliminary engineering design, surveying, and permitting to replace a failed 1929 box-culvert bridge, fish ladder, and degraded rock weirs at the Old Adobe Road crossing of Adobe Creek with a new clear-span bridge, restoring passage for federally threatened Central California Coast steelhead in the Petaluma River watershed, Sonoma County.
Location: Adobe Creek at the Old Adobe Road crossing within Petaluma Adobe State Historic Park, near Petaluma, Sonoma County. Adobe Creek (also called Casa Grande Creek) rises on Sonoma Mountain and runs roughly 7.5 miles to its confluence with the Petaluma River, part of the larger San Francisco Bay watershed.
Historical Fish Presence: Central California Coast steelhead (Oncorhynchus mykiss), with Chinook salmon, Pacific lamprey, eulachon, and threespine stickleback. The creek’s headwaters contain some of the only high Intrinsic Potential habitat in the entire Petaluma River watershed, though steelhead numbers have declined sharply from historical abundance due to blocked access to spawning and rearing habitat.
Project Lead: Sonoma County Public Infrastructure
Project Partners: California State Parks (landowner and co-funder), California Department of Fish and Wildlife (technical advisor), NOAA/NMFS (technical advisor), CalTrout (NGO advisor), United Anglers of Casa Grande/Casa Grande High School (community supporter and outreach partner), and Sonoma State University’s Anthropological Studies Center (cultural resources contractor).
CFPF Funding: $132,000 requested and awarded as part of the Forum’s FY2025 funded projects, toward a $322,000 total project cost. California State Parks is contributing $295,000 in matching Cannabis Watershed Protection Program funds for design and cultural studies on the portion of the project within park land.
Project Description: The 1929-era box culvert/bridge at Old Adobe Road sits offset from the creek’s natural thalweg, producing unnatural flow patterns, high velocities, and a perched outlet; its in-structure fish ladder and a downstream system of vortex rock weirs have both failed, causing annual stranding and death of juvenile steelhead for more than a decade and impeding passage across a range of flows. The barrier is a Priority 1 action (PR-CCCS-5.1.1.5) in NOAA’s Central California Coast steelhead Recovery Plan and appears on CDFW’s Fish Passage Priorities list. This grant funds preliminary engineering, surveying, geotechnical and hydrologic design, and cultural resources investigation needed to replace the structure with a new clear-span bridge that restores natural grade and volitional passage for all steelhead life stages, while also improving pedestrian and bicycle safety along the roadway.
Expected Completion: The design and permitting work funded by this award is expected to be completed within two years of funds arriving in spring/summer 2025, with construction funding and scheduling to be pursued in a later phase.
Project Effectiveness: Once built, effectiveness will be assessed using NOAA Restoration Center metrics and two to five years of post-construction monitoring of structure condition, channel stability, hydrologic function, and revegetation, alongside annual fish population surveys already conducted by Casa Grande High School’s United Anglers program.
