The Annenberg Wildlife Crossing over the 101 Freeway entered its final phase of construction this week, as crews prepare to build a secondary bridge over an adjacent smaller road.

The Agoura Hills wildlife freeway crossing is the largest of its type in the nation and was constructed to make it safe for animals to traverse from the Santa Monica Mountains to the Sierra Madre Range. The bridge, made with 26 million pounds of concrete, is intended only for animals and will be off-limits to humans.

Crews are now preparing to build a smaller bridge over Agoura Road, which will add to the crossing's span across the 10 lanes of the freeway. Project leaders say the Agoura Road bridge build, although much smaller, is more complex as it requires more "earthwork."

"The Agoura Road structure spans a smaller two-lane local road, but is as wide as the structure over the 101 freeway—and requires a more extensive foundation," organizers wrote in a news release. The width of the bridge equals five to six lanes in each direction, if it were designed to carry traffic, according to Caltrans.

As part of the Agoura Road build, a series of utility lines parallel to the freeway will have to be relocated.

In April, soil was laid on the 101 Freeway crossing in preparation for thousands of native plants to create a nearly one-acre wildlife habitat. Organizers said planting was supposed to take place this spring, but supply-chain issues and construction scheduling led to a fall planting schedule.

While the passing will support a variety of wildlife, including deer, bats, desert cottontails, bobcats, native bird species, and monarch butterflies, its primary inspiration was the mountain lion.

"This crossing will save the local mountain lion population from extinction, stand as a global model for urban wildlife conservation – and show us that it's possible for a structure of this magnitude to be built in such a densely populated urban area," Beth Pratt, California regional executive director of the National Wildlife Federation, said earlier at the onset of construction.

Researchers have estimated that the mountain lion population in the Santa Monica Mountains could become extinct within 50 years as freeways limit their movement across the region.

Los Angeles's famous feline, P-22, had to be euthanized in 2022 from what animal care workers described as chronic health problems and too many severe injuries, suspected to be linked to a vehicle strike. P-22 was famously known for roaming through the Hollywood Hills and Griffith Park area.

Work on the wildlife crossing began in 2022 and is scheduled to be completed in 2026. 

"To see the Wallis Annenberg Wildlife Crossing enter its final phase and near completion means we are closer to having that first mountain lion cross the bridge. I cannot wait to see that first photo of a cougar on the crossing — what a moment that will be for us all," Pratt said.