Project Crews Are Ready to Place the Very First Layers of Soil Over the Surface of the Wallis Annenberg Wildlife Crossing
Placement of the first layers of prepared soil over the surface of the crossing will launch what will be a nearly 1-acre native wildlife habitat across the 101 freeway.
Agoura Hills, Calif. (March 27, 2025) – The #SaveLACougars campaign is celebrating a new and exciting milestone on the journey to complete the Wallis Annenberg Wildlife Crossing. Next week, project construction crews will begin placing the very first layers of prepared soil over the surface of the crossing – launching what will become a nearly 1-acre native wildlife habitat across ten lanes of the U.S. Highway 101 freeway in the City of Agoura Hills.
When it’s completed, this visionary wildlife crossing will help wildlife travel safely across one of the busiest highways in the country, enhance motorist safety, restore local biodiversity, expand refuge for critical pollinator species, and help prevent the extinction of the local mountain lion population.
This latest project milestone is the result of years of meticulous work envisioned by the project’s landscape architecture team with the goal to create a native soil that will help plant life flourish. The effort required close collaboration with the team’s soil scientists, biologists, engineers, and mycologists who identified, harvested, and cultivated native soil biology and beneficial fungi from the site. Covering the entire surface of the crossing will require approximately 6,000 cubic yards of soil and will take several weeks to complete. Soil placement will be followed by the planting of about 5,000 native plants that will grow into a rich habitat that will support mountain lions, deer, bats, desert cottontails, bobcats, native bird species and monarch butterflies, to name a few. Weather permitting, planting is expected to begin in May.
The habitat on the bridge will be comprised exclusively of coastal sage scrub plant species native to the Santa Monica Mountains and, as part of the crossing’s restorative design approach – is part of a broader ecological restoration strategy that will revitalize an additional 12 acres of open space and require an additional 50,000 native plants, including native trees, shrubs, and perennials.
“I imagine a future for all the wildlife in our area where it’s possible to survive and thrive and the placement of this first soil on the bridge means another step closer to reality,” said Wallis Annenberg, Chairman, President and CEO of the Annenberg Foundation. "This extraordinary structure will serve not only animals, but it will reconnect an entire ecosystem and protect this global biodiversity hotspot - this moment marks another wonderful milestone toward that goal.”
“This long-awaited milestone launches a new chapter the remarkable decades long story of the Wallis Annenberg Wildlife Crossing. To get here, we built upon the forethought and resolute persistence of local advocates, were guided by the meticulous research of brilliant National Park Service biologists and enjoyed a deep collaboration with experts in their respective fields of study,” said Robert Rock, of Rock Design Associates. “We’re excited to see this modest slice of vegetation spring from the top of the crossing because it will serve as the vanguard for a broader plan that aims to expand the unique ecosystem that is the Santa Monica Mountains.”
“Wildlife crossings are unique because they allow people and nature to thrive together.” said Gloria Roberts, District Director, Caltrans District 7 of Los Angeles and Ventura counties. “By building the Wallis Annenberg Wildlife Crossing, Caltrans is supporting transportation infrastructure that will not only reconnect and restore habitats but also reduce vehicle collisions with wildlife and enhance highway safety.”
"Soil is the stuff of life and the success of a wildlife crossing relies on a healthy landscape layer and that starts with the soil!” said Nina-Marie E. Lister, Professor and Director of the Ecological Design Lab at the Toronto Metropolitan University. “Unlike the engineered bridges that are so familiar to people living in urban cities all over the world, the Wallis Annenberg Wildlife Crossing will not only have a technically designed surface that is supported by science – but also a surface that is very much alive and that will support future plant communities in the Santa Monica mountains and the wildlife that need and depend on a reconnected ecosystem.”
“The soil being placed on the crossing is such an exciting milestone! When the 101 freeway was built, it isolated the entire Santa Monica Mountains. As the long-term research from the National Park Service has demonstrated, this impacts wildlife large and small, even threatening the local mountain lion population with extinction,” said Beth Pratt, California Regional Executive Director for the National Wildlife Federation. “We are committed to designing this wildlife crossing with a habitat that will benefit everything from mountain lions to monarch butterflies to ensure all wildlife in the Santa Monica Mountains have a future. I love that even a freeway is redeemable ecologically!”
Another critical element in the ecological restoration are the ongoing efforts at the wildlife crossing’s dedicated native plant nursery. Over the last three years, nursery staff have hand-collected well over 1.1 million hyper-local native seeds representing over 50 distinct native plant species in the Santa Monica Mountains. The native plants, soil biology and seeds that have been collected until now, were all sourced from within a 5-mile radius of the crossing.
In preparation for future planting efforts, staff have also started growing plant and tree species including coast live oak trees, valley oak, toyon, ceanothus, several sages, California buckwheat and the flowering penstemon, to name a few. The soil amendment that will be used to restore a health ecosystem on top of the wildlife crossing is also being applied to the plants and trees at the project nursery. The restoration of native plants across the landscape also helps reduce fire risk—along with the full irrigation and sprinkler system that is part of the crossing structure.
The plant nursery is a critical part of the Wallis Annenberg Wildlife Crossing—funding for the nursery has been made possible by the National Wildlife Federation’s #SaveLACougars campaign and is located on land donated by the Mountains Recreation and Conservation Authority. Overseen by the landscape architecture practice that leads every aspect of the crossing’s design: Rock Design Associates, work at the project nursery is being advanced by experts from the Santa Monica Mountains Fund, the National Park Service, Caltrans, and the Mountains Recreation and Conservation Authority.
Work on the wildlife crossing began on Earth Day 2022 and is scheduled to be completed in 2026. Once finished, the Wallis Annenberg Wildlife Crossing will be the largest bridge of its kind in the world and a global model for urban wildlife conservation. The project is the result of a public-private partnership of unprecedented scope that has leveraged the world-renowned expertise and leadership of dozens of individuals, organizations, and institutions.
