Wildlife Bridge Near L.A. Reconnects Mountain Lions

Could a massive overpass above ten lanes of busy freeway be a lifeline for mountain lions? Near the bustling Los Angeles region, a team of conservationists, engineers, and local stakeholders is proving yes. In Agoura Hills, California, construction has reached a milestone on the Wallis Annenberg Wildlife Crossing, an ambitious project built to help mountain lions, deer, bobcats, and many other species roam freely between the Santa Monica Mountains and Simi Hills. Its goal: rescue an entire ecosystem from fragmentation and give wildlife a future in the country’s second-largest metro area.

Roadblocks for Mountain Lions

Researchers have studied the Santa Monica Mountains area for over two decades, discovering that freeways have isolated mountain lions in small pockets. With limited territory to roam and mate, this cougar population faced the risk of inbreeding and decline. The 101 Freeway, in particular, was the biggest barrier, effectively cutting off the Santa Monica Mountains from habitat to the north.

The need to fix this fragmentation gained urgency in late 2022, when Los Angeles’s famous cat, P-22, died from injuries tied to a suspected vehicle strike. He roamed Griffith Park alone for a decade, and his story drove home the isolation these big cats face. According to National Park Service Superintendent David Szymanski, “Twenty years of research shows that the biggest challenge for our local wildlife is isolation by roads and development. This crossing will help end that isolation.”

A Ten-Lane Challenge

What makes this project so remarkable is the size of the 101 in Agoura Hills—a corridor that carries more than 300,000 cars daily. Through an innovative design, the overpass stretches 165 feet wide and about 210 feet long, enough space to accommodate oak trees, native shrubs, and even a winding wildlife pathway that feels natural to animals. This living overpass aims to drown out city noise with tall walls and thick vegetation, so that crossing animals hardly realize they’re going over a freeway.

Construction reached a milestone as workers began laying the first layers of soil. Over the next several weeks, 6,000 cubic yards of dirt will spread across the bridge, then be planted with sage, buckwheat, wildflowers, and, eventually, larger trees. This “living roof” will mirror the local ecosystem, allowing animals to pass from one side to the other in relative quiet and safety.

Creating a Biodiversity Bridge

The project stems from a partnership among Caltrans, the National Park Service, the Santa Monica Mountains Conservancy, the National Wildlife Federation, and many others. Private donors and philanthropic groups contributed as well. The Annenberg Foundation, led by Wallis Annenberg, supported a large part of the effort:

“This extraordinary structure will reconnect an entire ecosystem,” Annenberg said. “Protecting this global biodiversity hotspot is our best chance to preserve these remarkable animals for future generations.”

The crossing is named for her major conservation gift, which rallied public and private funding to push the idea from blueprint to groundbreaking.

Saving More Than Lions

Though mountain lions got the headlines, the bridge is about more than big cats. It reopens a corridor for deer, cottontails, bobcats, lizards, native birds, and pollinators such as monarch butterflies. Scientists expect it to boost diversity for everything from predators to smaller creatures. As Beth Pratt, the National Wildlife Federation’s California Director, explained, “This crossing will save the local mountain lion population from extinction and stand as a global model for urban wildlife conservation.”

Since the Santa Monica Mountains have a wide range of habitats—from chaparral to coastal sage—pockets of flora and fauna are stuck in “islands” of safe land. This crossing ensures that animals have access to a wider territory, crucial for survival, genetic health, and resilience to climate shifts. Over the years, local groups worked to preserve thousands of acres of open space, and the wildlife bridge is the final link that ties those areas together.

Designing for Nature

Building a structure that feels natural to wildlife requires a careful approach. Engineers and biologists teamed up to:

1. Reduce Noise: Tall walls buffer traffic sounds, letting animals relax as they cross.
2. Recreate Soil Biology: Experts collected local soil, fungi, and seeds so the crossing’s environment mimics the nearby terrain.
3. Set Up Fencing: Fences guide animals to the crossing, rather than letting them wander into traffic.
4. Ensure Longevity: Constructed with 26 million pounds of concrete, the overpass stands 21 feet above the highway. Its design aims to last for many generations.

Several nights, crews partially closed the 101 to place massive girders. Then the surface was carefully layered with subsoil, topsoil, and plantings. In the second project phase, a companion section will cross Agoura Road, and an additional 12 acres of open space on either side will receive thousands of native trees and shrubs.

A Tribute to P-22

While the crossing won’t benefit the Hollywood lion himself, P-22 remains a symbol of what’s at stake. He famously crossed the 405 and 101 Freeways, living alone in Griffith Park for over a decade. At the time, many were amazed he survived such a risky trek. His story is a reminder that Los Angeles is truly “where the wild meets the urban.” The local puma population, however, needs a safer, more consistent route. By bridging this gap, future cougars can roam, mate, and keep the species strong.

Timeline and Future Impact

With a final price tag of about $92 million, the project broke ground on Earth Day 2022. Rain and flooding delayed progress in recent years, shifting completion to 2026. But watchers say the payoff is enormous. As mountain lions roam beyond the Santa Monica Mountains, they’ll mix with other populations in the Simi Hills, Santa Susana Mountains, and even the Los Padres National Forest, potentially reversing signs of inbreeding. Other species, from insects to reptiles, can also move more freely, improving the region’s overall ecological health.

This is vital for a biodiversity hot spot like Southern California, where multiple endangered species live. Connecting areas also helps wildlife adapt to droughts, wildfires, and future climate changes. Freed from isolation, animals can find new food sources or safer shelter when faced with environmental stress.

Building a Legacy

Southern California is known for congested freeways, suburban sprawl, and star-studded cityscapes. So, constructing a giant wildlife overpass might feel bold. Yet supporters see it as an emblem of a city evolving to welcome nature. Los Angeles County, home to 10 million people, has shown surprising readiness to champion an ecological initiative that decades ago would have been dismissed as impossible.

Local leaders say the crossing addresses more than a wildlife issue. The California Natural Resources Agency calls it a prime example of “nature-based solutions,” showing how cities can reconnect habitats for the good of all. If successful, it could spur other urban areas to follow suit, bridging roads and freeways to link habitats. Already, 50 other projects across the country are looking to replicate lessons from L.A.

Getting Involved

If you want to support this historic effort, you can:

1. Donate: The #SaveLACougars campaign from the National Wildlife Federation continues to gather support for ongoing research and habitat stewardship.
2. Volunteer: The project’s partners, including the Santa Monica Mountains Fund and Caltrans, have docents who track progress and help with outreach.
3. Learn: You can follow the crossing’s live camera feed or sign up for tours to see the overpass in action (visits occur on designated days).
4. Plant Native Species: Landowners in nearby areas can add local flora that extends habitat corridors right from their backyards.

A Model for the World

It’s rare for a single construction project to bring so much optimism in both science and public imagination. But the Wallis Annenberg Wildlife Crossing, once only a dream among local conservationists, stands as a giant leap for mountain lions and a statement that humans and wildlife can coexist. As Wallis Annenberg says, “These crossings go beyond conservation, toward a kind of environmental rejuvenation that is long overdue.”

That rejuvenation starts with reconnecting one of North America’s most congested landscapes. It’s a hopeful vision for cities worldwide facing similar challenges: we can reverse fragmentation and write a new story of people and wildlife thriving together.