With physical construction done, the project moves to the planting stage. The one-acre habitat bridge will connect long-isolated wildlife areas of the Santa Monica Mountains.
Three years after construction began, it’s time to dump dirt on the project. Specifically, 6,000 cubic yards of a “super” soil followed by the planting of 5,000 native flora. I’m talking about the world’s largest wildlife crossing, which has reached another construction milestone as the bridge nears completion.
This prepared soil is the beginning of the end of construction for the Wallis Annenberg Wildlife Crossing, which broke ground on Earth Day in 2022. Located in Agoura Hills, California, the nearly one-acre overpass stretches over a 10-lane section of U.S. 101.
The physical bridge structure is essentially complete, having required 26 million pounds of concrete, Beth Pratt of the National Wildlife Federation (NWF) told KCAL. The NWF Regional Executive Director added, “We just put the soil on top, and then we start burying utility lines and extend it over the access road.”
Multiple layers of soil will be needed to create a wildlife habitat on the overpass, and the soil application alone will take several weeks. However, when the Annenberg Wildlife Crossing is done, the bridge will reconnect the bisected areas of the Santa Monica Mountains National Recreation Area. With more than 150,000 acres, SMMNRA is the country’s largest urban national park. But the freeways have long isolated the local fauna, from butterflies and cottontails to bobcats and mountain lions.
According to the project, as far back as the 1980s, researchers identified the Liberty Canyon area as a choke point for wildlife. However, it wasn’t until the National Park Service began a decades-long study of the region’s mountain lion population that the 101 freeway was deemed “the most significant barrier to the ecological health of the region.”
More than 300,000 vehicles travel along U.S. 101 daily. That’s enough traffic to give a driver anxiety—try being a local critter having to dart across the road just to find dinner.
P-22, arguably the most famous mountain lion in and outside of Hollywood, surprised everyone by crossing freeways on his own. He eventually became the poster cat for the “Save L.A. cougars” campaign. Unfortunately, he was euthanized in late 2022 after being found with severe injuries, likely due to a vehicle collision, and a myriad of other health issues.
Mountain lions are the main conservation focus of this wildlife bridge. The big cats are territorial, and being locked in by freeways limits their roaming range and biodiversity. Without the crossing to expand their habitat, SoCal cougars could be extinct within 50 years. They also continue to be killed by vehicles.
“In the Liberty Canyon area where we’re putting the crossing, within the last four years, we’ve had four mountain lions killed just in that general area,” Pratt said.
Not just providing access to more sources of food, shelter, and mates, but the bridge would also offer an escape route from wildfires and other disasters. The Annenberg Wildlife Crossing is expected to reach completion next year.
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Comments
By jedberg 2025-06-2215:39 I grew up in Agoura Hills, it's funny to see this on HN of all places. And in another amusing twist, I just drove under this two days ago because I am visiting my parents this weekend.
It's something the locals have known was needed for a long time, I'm glad they were finally able to get it built.
By jonstewart 2025-06-2212:271 reply Introducing wolves back to a relatively small part of Wisconsin has had a positive economic impact from reduced car crashes with deer. This crossing will no doubt help the cougars, and that’ll help the humans who have to drive on this terrifying part of the 101.
https://wolf.org/media-releases/new-study-shows-wolves-save-...
By rurp 2025-06-2217:56 One of my favorite wildlife stats is that you're hundreds of times more likely to be killed by a deer than a mountain lion. Protecting apex predators like wolves and lions significantly reduces deer caused deaths and injuries. It's nice to see public opinion steadily changing in this area for the better, past predator management has been extremely stupid and harmful.
By michaelrmmiller 2025-06-2214:571 reply I live nearby and drive past it nearly every day. It’s been fascinating watching its construction. They’ve done a very good job not impacting traffic and only closed down the highway late at night for a week or two.
Yeah! The first time seeing it was funny, a bridge with no roads. Excited for it to open. It’s a bummer that it cost $100m
By WalterBright 2025-06-2217:591 reply At those costs, very very few will be built.
More modest projects should be considered. Like simple bridges, or large culverts running underneath the highway.
I wonder why they didn't opt for your suggestion for multiple modest projects.
The article doesn't mention it, it only says:
> National Park Service began a decades-long study of the region’s mountain lion population that the 101 freeway was deemed “the most significant barrier to the ecological health of the region.”
By eszed 2025-06-2221:22 A big reason (this is from the project site):
> NEPA Completed 04/12/2018: Finding of No Significant Impact (FONSI), Liberty Canyon Wildlife Habitat Connectivity Project
> In compliance with CEQA, Caltrans held a 47-day public scoping period to allow the public and regulatory agencies an opportunity to comment on the scope of the IS/EA and to identify issues that should be addressed in the environmental document. A scoping report documents the issues and concerns expressed during the public scoping meetings held on January 14, 2016 and the written comments received from the public, community organizations, and governmental agencies during the public scoping period from December 14, 2015 through January 29, 2016. The release of the Final Environmental Document with responses to comments included was completed in the summer of 2016. NEPA/CEQA was completed in April 2018. A total of 8,859 comments were received in response to the draft Environmental Document, with only 15 opposed.
When any infrastructure project requires nearly a decade of preliminary work before shovels hit ground, said work becomes impossible to accomplish for smaller-scale builds. Even if ten smaller bridges would be a better solution, 10x-ing the review process would likely be impossible at current staffing / budget levels.
It's a big problem.
By Espressosaurus 2025-06-2221:25 If it's too small/unsafe you'll end up with wildlife not using it or being funneled in for other for predators. The larger and more skittish the animals you want to use it, the larger you're going to want to make it. Since they're calling out mountain lions, which are quite skittish, they're going to need a large (and probably partially covered) pathway for them to want to use it--as opposed to treating the freeway like the barrier it is to wildlife.
I'm sure there's more to it than that, but making it desirable, accessible, and for it to feel safe for the target animal population is important for it to accomplish what it's intended to do.
There are smaller culverts all over the place for smaller wildlife. I've even seen some called out in small walking paths--there for the frogs and other amphibians.
By unstatusthequo 2025-06-2319:55 That’s truly an unbelievable amount. I suppose there is some breakdown of this available. Would love to hear from someone who knows on the actual reasonableness of the costs. Seems exceptionally out of line from the sidelines.
