By LaTresa Pearson
I feel as though I’ve just passed through a magical portal. One moment, I’m walking across a gravel parking lot for San Diego’s Los Peñasquitos Canyon Preserve, accompanied by the hum of traffic from the nearby roads and freeways. The next, I’m enveloped by western sycamore trees, coast live oaks and arroyo willows.
The traffic noise recedes into the background, succumbing to the bubbly song of a house wren and the burbling of the nearby creek. I pause to watch the wren as he darts to the ground to grab a twig. It’s nesting season, and he’s busy trying to woo a mate and start a family.
As I witness this spring ritual, I’m reminded that this preserve, and many others like it, serves as a home to hundreds of species of plants and animals, while also providing us with a place to escape from the stressors of daily urban life.
These pockets of nature exist in canyons throughout Southern California, partially because their topography makes them challenging to develop, but also because communities have fought to keep them here, valuing the ability to connect with nature in their own neighborhoods.
These are not just pretty spaces. Urban canyons work hard. They absorb and filter stormwater, leaving our oceans and everything downstream cleaner. They reduce temperatures in our cities. They improve air quality. They provide habitat and corridors for wildlife. And they give us places for recreation and connection to nature, and the whole slew of health benefits that go along with that — less anxiety and depression, better sleep, better focus and problem-solving skills, less chronic disease and longer life spans.
From the massive Santa Monica Mountains National Recreation Area in northern Los Angeles County to neighborhood canyons like Runyon Canyon in Los Angeles and Eaton Canyon in Pasadena (both heavily impacted by January’s wildfires), to mid-sized parks like the Sycamore Canyon Wilderness Park in Riverside and the Aliso & Wood Canyons Wilderness Park in Laguna Niguel, Southern California offers an amazing array of natural spaces that are easily accessible to residents and visitors alike.
San Diego’s wild side
Nowhere, however, will you find more undeveloped urban canyons spread throughout a city than in San Diego. According to the San Diego Natural History Museum (The Nat), more than 80 percent of the city’s 1.4 million residents live within a 10-minute walk of a park or green space, and this is largely due to urban canyons.
There are hundreds of urban canyons spread throughout the county, some 27,000 acres of which are managed by the Open Space Division of the city of San Diego’s Parks and Recreation Department. These lands snake through the city from as far north as San Pasqual and Clevenger Canyon near the San Diego Zoo Safari Park all the way down to Otay Valley Regional Park near the southern border.
“If you go to the city of San Diego’s website, there’s a map, and you can see all the little slivers of neighborhood canyons and open space parks within five miles or less of your house,” says Julie Aeilts, senior park ranger for Mission Trails Regional Park, an 8,000-acre open space park located just 8 miles northeast of downtown San Diego. “We really want people to know what treasures they have in their own backyards.”
Part of what makes the city’s urban canyons such treasures is they provide important habitat and corridors for San Diego County’s plants and animals, including 85 species that are either endangered, threatened or species of concern. The county is the most biodiverse county in the continental U.S., but it is also a “biodiversity hotspot.” That means its biodiversity is not only recognized as globally important, but it is also severely threatened — making it vital to conserve the biodiversity that remains in the county.
“We have so many special species here,” says Aeilts. “We have San Diego fairy shrimp, the California gnatcatcher, the Least Bell’s vireo, burrowing owls — all kinds of wonderful animals — and plants, such as San Diego thornmint and San Diego ambrosia.”
More understanding needed
One of the challenges of conserving the biodiversity in San Diego’s urban canyons is there isn’t enough known about the species living in them.
“We definitely need a baseline of just understanding what species are there,” says Rachel Larson, a postdoctoral researcher in The Nat’s Conservation Biology Department and one of three researchers spearheading the museum’s Healthy Canyons Initiative, a multiyear project to survey the plants and animals living in 20 different urban canyons throughout the county.
The researchers hope the surveys will help determine the state of conservation of plants and animals in the canyons and empower community members — whether they are land managers, policymakers or local residents — to become stewards of these spaces.
All of The Nat’s departments — including Birds and Mammals, Entomology, Herpetology, Botany and even Paleontology — are conducting extensive fieldwork at the 20 sites, collecting data on a wide range of species. “Something that makes this project unique is the fact that it involves all the taxonomic disciplines in our museum, which gives us really cool overlapping data,” says Larson.
This multidisciplinary approach means researchers can look beyond what’s happening with specific species and begin focusing on wildlife communities.
“That is a really interesting move forward for the field of urban ecology because a lot of it has been species-focused,” she adds. “We can look at how plants and animals interact with each other and how the urban fabrics might shift those interactions and what that means for ecological processes.”
A southern mule deer at Los Peñasquitos Canyon Preserve on Tuesday, April 1, 2025 in San Diego, California. (Ana Ramirez / The San Diego Union-Tribune)
Every picture tells a story
With a background in mammalogy, Larson has one of the coolest jobs in the project. She’s in charge of the large mammal camera traps designed to capture images of the variety of mammals living in the canyons. She currently has 37 cameras deployed in the field, with at least one camera in each of the 20 target sites in the Healthy Canyons Initiative.
She sets the cameras out on a quarterly basis (October, January, April and July), and each camera stays at a site for about a month. She started deploying the cameras in October of last year and was just about through the April cycle at press time.
One of the cameras captured a mountain lion in the Elfin Forest Recreational Reserve in Escondido on two separate occasions.
“They basically go wherever there’s enough space to support deer,” says Larson. “That’s the one thing mountain lions tend to care about. It was cool to see that individual had stayed in the canyon. Hopefully it establishes territory there and we see it often, but if it is a juvenile, it may disperse out of it at some point. They don’t tend to stick around.”
Some of her favorite images so far are of a gray fox captured by a camera in Tecolote Canyon. “It was really cute,” says Larson. “He’s staring directly into the camera.” She says she had a bobcat do the same thing in Los Peñasquitos Canyon. “He was taking selfies, just staring into the game camera,” says Larson. “We think they can hear the shutter shut, but they don’t seem afraid.”
One of the more dramatic captures by one of the cameras was a barn owl trying to grab a wood rat sitting right in front of the camera. “I’m not sure whether it was successful or not,” she says. “There was just like a flurry of wings, and the owl kind of sat for a second before flying off.”
Recording sessions
In addition to cameras, researchers are also deploying audio recorders in the target canyons to monitor species of birds and bats. “The bird recorders are a really cool way the public can get involved,” says Olivia Poulos, The Nat’s community engagement manager. “If you live within 1,000 meters of one of the selected canyons, we would love to have a bird recorder in whatever outdoor space or yard that you may have.”
Larson says they are pairing audio recording devices, so one device will be deployed in the canyon, and the other device will be deployed in the neighborhood that borders the canyon. People who host a recorder will receive a report listing the species of birds recorded in their yard as well as a list of species picked up by the paired recorder in the canyon.
“Hopefully as a result of the science, we might be able to explain why you only see certain species in some places,” says Larson. “Homeowners can decide what they want to do with that information like whether they might want to make changes to their landscaping to attract more birds.”
How to help
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Even if you don’t live right next to one of the 20 canyons in the museum’s Healthy Canyons Initiative, you can still help researchers document the plants and animals living in them by joining the project on iNaturalist and submitting observations either through the smartphone app or on the iNaturalist website.
“You don’t need to be an expert,” says Poulos. “The beauty of the app is it can connect you with our scientists. They are on the app helping to identify species that you photograph.”
Larson points out these iNaturalist observations are vital to the project because the museum’s researchers can’t be out in all 20 canyons every day. “They really do add to the rigor of our scientific models and give us a lot more information about where species are,” she says.
While they receive a lot of observations from the larger canyons and open space parks, such as Mission Trails, Los Peñasquitos Canyon and Tecolote Canyon, they would like to receive more observations from the smaller canyons.
“There are fewer iNaturalist sightings from certain neighborhoods where people don’t have as many resources and time to go out and take those observations,” says Larson. “I get it if you work two jobs and recreating outside is not something that is in the cards for you, but maybe you can snap a photo of something while walking the dog. Even that adds so much natural history value to your neighborhood and the greenspaces by it.”
Larson also emphasizes that you don’t need to just document rare or unusual plants and animals. “Even common species observations have a ton of value,” she says. “We can really start raising alarm bells if we suddenly see drops in common species. If it’s affecting the common species, it’s definitely affecting the rare ones.”
Millie Basden is one of the community scientists participating in the Healthy Canyons Initiative. As an avid iNaturalist user, she regularly submits her observations to the project and enjoys the interaction she has with scientists and other iNat users.
“Some of the plants I’ve found, I didn’t know what I’d found,” says Basden. “I put them on iNaturalist, and Jon Rebman [curator of The Nat’s Botany Department] came along and said, ‘Wow! I didn’t know that was out there!’”
As a resident of Tierrasanta, Basden frequently explores the West Fortuna side of Mission Trails, which is just a short walk from her house. She has become very familiar with the plants and animals there and has even discovered species of plants that had never been identified in the park. Basden, who volunteers in The Nat’s Botany Department, says she was able to collect specimens and take them to the museum’s herbarium, and they will be added to the park’s plant checklist. “I feel a real sense of ownership for this side of the park,” she says.
That sense of ownership is something many regular visitors to San Diego’s urban canyons experience, and it’s something Larson hopes the Healthy Canyons Initiative will inspire in those who have yet to discover these community treasures.
Los Peñasquitos Canyon Preserve is where I experience that sense of ownership. As I wander along Peñasquitos Creek through the western sycamore trees, arroyo willows and coast live oaks, listening to the birds sing and the water tumbling gently over the rocks, I feel at home.
Resources
Open Space Canyons and Parklands, City of San Diego
San Diego Natural History Museum’s Healthy Canyons Initiative
Friends of Los Peñasquitos Canyon