Petersen Ranch Mitigation Bank

The Petersen Ranch Mitigation Bank, encompassing 4,236 acres in Los Angeles County, is the largest mitigation bank in California. The bank consists of two different sites: the 3,919-acre Petersen Ranch near Leona Valley and the nearby 317-acre Elizabeth Lake site.

Restored Alluvial Fan habitat at Elizabeth Lake two years after construction was completed.

The Elizabeth Lake site is unique in that the restoration program called for restoring an alluvial fan by lowering a historic sediment dam at the mouth of Munz Canyon. We believe this to be the first full restoration of an alluvial fan. The design called for reinforcing the dam with riprap and spreading flows over a 70-acre downstream area to restore desert alluvial fan habitat. In addition, the spoils area was graded to create a naturalistic landform and seeded with native species to blend in with the landscape and maintain aesthetics of the adjacent Elizabeth Lake recreation area. WRA developed a novel crediting methodology for this project to facilitate a process based restoration approach, where habitats would evolve over time.

WRA Spring 2017 drone image of Petersen Ranch wetland restoration during construction.

The Petersen Ranch site involved removing man-made hunting ponds in the Rift Valley wetland complex and restoring the historic wet meadow wetland community. Specific habitats targeted included seasonal wetland, wetland riparian, and non-wetland riparian. The design restored the natural valley floor landform and incorporated existing ranch roads and infrastructure to maintain the function of the working cattle ranch and improving aesthetics for existing and future owners. More than 150,000 native wetland and riparian plants were installed for this restoration project. Restoration was completed in the spring of 2017, and WRA is actively managing and monitoring the site to ensure compliance with performance standards.

WRA managed the Bank from site selection through the entitlement phase, and continues to manage bank operations today. WRA led the conceptual restoration planning tasks and authored bank entitlement documents. WRA performed all of the biological baseline field studies (biological Resources Inventory, vegetation mapping, wildlife and rare plant surveys, wetland delineation and CRAM. WRA coordinated bank approval with the Los Angeles District of the U.S. Army Corps of Engineers, U.S. Environmental Protection Agency, South Coast Region of the California Department of Fish and Wildlife, and the Lahontan and Los Angeles Regional Water Quality Control Boards. WRA manages credit sales and reporting for the Bank.

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