Rio Del Oro

The 3,893-acre Rio del Oro specific plan is located within the City of Rancho Cordova, Sacramento County, California. Significant portions of the property were mined for gold starting in the early 1900s and the remainder was used primarily for agriculture. ECORP Consulting Inc. provided biological, cultural, and regulatory permitting services that covered a wide range of issues.


ECORP completed the wetland delineation for this complicated site. The delineation had to address Rapanos Analysis to determine which wetlands were “isolated” and which were under the jurisdiction of the U.S. Army Corps of Engineers. The isolated wetlands are primarily located in between the tailings piles left from the past mining. Here, fine particles of soil that settled after mining ceased created a place for wetlands to re-establish. In addition, blue elderberry shrubs (Sambucus mexicana) flourished (over 300 shrubs were located within the project site) in the highly disturbed post-mining conditions leading to consultation with the U.S. Fish and Wildlife Service (USFWS) regarding the Valley elderberry longhorn beetle (Desmocerus californicus dimorphus) and the preparation of a suitable mitigation plan. The tailings piles primarily consist of cobble with limited vegetation outside of the wetland areas. ECORP performed a study that assessed the tailings and associated grasslands’ suitability for providing prey for foraging raptors, specifically Swainson’s hawks (Buteo swainsoni) and to determine if it would be appropriate to mitigate for loss of foraging habitat as a result of the development of the site.


ECORP conducted rare plant surveys within the vernal pool complexes located in the southeastern portion of the site. Orcutt grasses (Orcuttia tenuis and Orcuttia viscida) are known from the vicinity. No occurrences were located. ECORP assisted the inter-agency team developing the California Rapid Assessment Method vernal pool assessment protocol by performing CRAM on Rio del Oro and providing feedback into the method’s development. Vernal pools will be restored, enhanced, and created within a 510 acre portion of the site that will be preserved. ECORP conducted fieldwork, assessed historic photos, and used LIDAR-derived topographic data to develop the vernal pool mitigation plan. The LIDAR-derived topographic data was also used to determine if the limits of the proposed preserve boundary are sufficient to maintain the hydrologic function of the existing and restored wetlands. After the Rio del Oro project has built out the wetland preserve will be managed according to a long-term management plan developed by ECORP to address the management, maintenance and monitoring of the preserved resources.


ECORP assissted the applicants and the USACE in compliance with Section 106 of the National Historic Preservation Act due to the presence of historic-era placer mining tailings and the historic military installations in the project area. ECORP first prepared a research design with sampling strategy that balanced previous studies with new requirements that developed during the time the project has been processing. ECORP negotiated the scope of the research design with the USACE and Office of Historic Preservation, and implemented the plan. Subsequently, we developed and executed a Memorandum of Agreement and Historic Property Treatment Plan for the resolution of adverse effects to the Douglas Missile Test Facility district, located within the project area.