They placed the first layers of soil on what will become a nearly 1-acre native wildlife habitat, and eventually grow across 10 lanes of the freeway in Agoura Hills. Covering the entire crossing will require about 6,000 cubic yards of soil and take several weeks to complete.
Work on the crossing began on Earth Day 2022 and is scheduled to be completed in 2026.
Once finished, the crossing will be the largest bridge of its kind in the world, and a global model for urban wildlife conservation, according to the National Wildlife Federation, America's largest conservation organization.
Officials described Monday's work as a milestone, resulting in years of meticulous work. The effort required close collaboration with soil scientists, biologists, engineers and mycologists who selected the best soil and beneficial fungi for the bridge.
After the soil is placed, the next leg of work is expected to be done in May, which includes planting about 5,000 native plants that will grow into a habitat for mountain lions, deer, bats, desert cottontails, bobcats, native birds and monarch butterflies, among others.
According to the NWF, coastal sage scrub plant species native to the Santa Monica Mountains will fill much of the bridge. It's part of a broader ecological restoration strategy that will revitalize an additional 12 acres of open space that requires 50,000 native plants, trees, shrubs and perennials.
Over the last three years, the wildlife crossing's dedicated native plant nursery has hand-picked more than 1.1. million hyper-local native seeds, representing more than 50 distinct native plant species in the Santa Monica Mountains.
Nursery staff have also started growing plants and tree species such as coast live oak trees, valley oak, toyon, ceanothus, several sages, California buckwheat and the flowering penstemon, among others.
Native vegetation will help reduce fire risk and better support wildlife. Crews are expected to implement a full irrigation and sprinkler system as part of the crossing.
The nursery is overseen by the landscape architecture company, Rock Design Associates, with aid from experts from the Santa Monica Mountains Fund, the National Park Service, Caltrans, and the Mountains Recreation and Conservation Authority.