World's largest wildlife crossing nears completion over California's Highway 101

What is the background?

US Highway 101 near Agoura Hills, California, cuts through habitat used by mountain lions, deer, and other wildlife moving between the Santa Monica Mountains and nearby ranges. Wildlife crossing California 101 projects like this one respond to years of documented roadkill and genetic isolation among local mountain lion populations that cannot safely cross the ten-lane highway.

What happened?

The Wallis Annenberg Wildlife Crossing entered its final construction phase in June 2025 and is scheduled to open to wildlife in fall 2026. When complete, it will be the largest wildlife crossing in the world, connecting open space on both sides of the 101 in Agoura Hills.

Phase one, completed in 2025, used 26 million pounds of concrete, 82 bridge girders, vegetated sound walls, and 6,000 cubic yards of living soil. Phase two, which began in June 2025, extends the crossing over a two-lane local road and includes earthmoving, hydrology restoration, and utility relocation.

How did it happen?

The project is a public-private partnership involving state and federal agencies alongside private donors and conservation groups. More than 50 native plant species will be planted across the crossing to recreate natural habitat that animals will actually use, rather than a bare structure they might avoid.

California Governor Gavin Newsom said the crossing would “protect Los Angeles’ native wildlife and over 300,000 drivers daily, as well as provide a cutting-edge model for urban wildlife conservation.”

Why does it matter?

Roads that fragment habitat do two kinds of damage: they kill individual animals in collisions, and they cut breeding populations off from each other, which over time reduces genetic diversity and makes local populations more vulnerable to disease or decline. A crossing this size addresses both at once, by giving animals a route that functions like real terrain rather than a narrow tunnel.

The project also protects the more than 300,000 people who drive this stretch of the 101 daily, since large-animal vehicle collisions are dangerous for drivers as well as wildlife.

What were the key results?

• Will be the world’s largest wildlife crossing when complete
• Spans all ten lanes of US Highway 101 in Agoura Hills, California
• Phase one used 26 million pounds of concrete and 82 bridge girders
• More than 50 native plant species will be planted to recreate natural habitat
• Expected to benefit more than 300,000 daily drivers on Highway 101
• Funded through a public-private partnership of state, federal, and private donors
• Scheduled to open to wildlife in fall 2026

What happens next?

Construction teams will complete hydrology restoration and utility relocation before the crossing opens in fall 2026.

Wildlife biologists plan to monitor camera-trap data after opening to measure how quickly animals begin using the crossing.

California conservation groups are using the project as a model for other proposed crossings on high-traffic highways in the state.

The Governor’s office said it will report on the crossing’s ecological impact once monitoring data is available after the fall 2026 opening.