Interstate 15 Rainbow Canyon Wildlife Crossing

Background

The California Department of Fish and Wildlife has designated Interstate 15 between the San Diego-Riverside county line and Temecula as one of the state’s top 12 priority wildlife barriers. This highway segment is a nearly impassable barrier to wildlife movement between the Santa Ana and Palomar Mountains, severing a habitat linkage that is essential for the long-term viability of wide-ranging species and those shifting their range in response to climate change. Mountain lions and other wildlife, including bobcat, coyote, mule deer, gray fox, ringtail, spotted skunk, and striped skunk have been documented by camera traps on both sides of the highway, but existing crossing structures are inadequate. As a result, the Santa Ana mountain lion subpopulation, in particular, is experiencing significant genetic restriction.

The Interstate 15 Rainbow Canyon Wildlife Crossing, a planned vegetated overcrossing, will reconnect this landscape, providing safe passage for a multitude of wildlife species continuing their path through a key climate corridor. The crossing will link the Santa Ana Mountains, via the Santa Margarita Ecological Reserve, to the Palomar Mountains and other protected areas within the greater eastern Peninsular Ranges region, restoring landscape-scale connectivity essential for ecological resilience. The Western Riverside Regional Conservation Authority (RCA) owns the property adjacent to I-15 to the west of the planned crossing location. This property is part of the Santa Margarita Ecological Reserve, which is composed of protected lands managed by San Diego State University. The Nature Conservancy (TNC) owns the property to the east of the highway at the proposed crossing site. RCA and TNC will cooperate with Caltrans District 8 and other project partners as needed to provide right of way for the crossing’s construction. 

In 2022, TNC convened an expert workshop to inform the design requirements for potential I-15 crossing structures. Experts considered elements such as vegetation cover, substrate type, and noise and light mitigation to meet the specific needs of mammals, birds, bats, plants, and invertebrates. The resulting design elements will result in a net gain of wildlife habitat and facilitate the movement of pollinators, birds, and less mobile species, while also creating potential live-in habitat for smaller wildlife. Overall, these design elements are expected to make the overcrossing suitable for at least 26 different species.

In response to wildlife mortalities, Caltrans District 8 constructed 3 miles of wildlife exclusion fencing along both sides of I-15, from the Temecula Creek Bridge (just south of the City of Temecula) to the San Diego County line, as part of a highway rehabilitation project. The fencing was finalized in 2022, and no mountain lions have been killed by vehicle strikes along this stretch of highway since fence construction was initiated, though genetic isolation persists.

In November 2024, Caltrans approved the Project Initiation Document (PID) for the overcrossing, a Project Study Report - Project Development Support. The PID contains further details on the proposed crossing design alternatives and expected needs and requirements in subsequent project development phases. In March 2026, TEAM RCD became the recipient of a grant from the State of California Wildlife Conservation Board (WCB) to continue the environmental permitting and design of the overcrossing. The current project funded by WCB will build on the PID to deliver completion of the PA&ED phase and PS&E to 35% and 65% design. 

Project Team and Partners
The Project Team includes TEAM RCD, TNC, Caltrans District 8, and Western Riverside RCA. TNC brings decades of experience in conservation science, land protection, and partnership building in the South Coast region, including managing complex conservation-oriented partnerships in the area. In this location, TNC has worked together successfully with partners, Including Western Riverside RCA, to protect hundreds of acres of land, develop a plan for the Santa Ana-Palomar Mountains Wildlife Linkage, and advance the planning of this proposed wildlife crossing. The Project Team will be responsible for project management and coordination with other project partners. TEAM RCD will be the primary project manager and will direct the scope of work to ensure deliverables are achieved on schedule. 

Project partners may include those organizations, agencies, and other entities that are consulted or informed throughout the process and asked for input/advice at key project checkpoints within their area of expertise. These partners will help to refine and review deliverables and provide valuable subject matter expertise and feedback on specific elements of the project. The Project Team will be responsible for seeking and consolidating input from partners on product deliverables and for convening meetings with partners.