Take the Edgewood Road exit off 280, and within a quarter mile you will pass two trailheads that most people treat as the same errand. Same rolling hills. Same oak canopy. Same instinct to grab the leash and go. But cross from one side of the road to the other and the rules flip entirely. On one side, your dog can run free in a fenced-off area with no leash at all. On the other, dogs are not permitted anywhere on the property, full stop, no exceptions for small dogs or short visits.
Most people who hike here regularly have absorbed this rule without knowing why it exists. It is not arbitrary, and it is not really about dogs. It is about what each piece of land used to be, and what one of them is still quietly trying to become.
A Sanitarium Becomes a Dog Park
Pulgas Ridge Open Space Preserve sits in the hills above San Carlos and Redwood City, and for most of the twentieth century it was not open space at all. It was the site of the Hassler Health Home, a tuberculosis sanitarium owned by the City of San Francisco. The Midpeninsula Regional Open Space District purchased the 366-acre property in 1983, and the sanitarium buildings came down two years later. If you know where to look along the Cordilleras and Hassler trails, you can still find the remains: rock retaining walls, old steps, foundations slowly disappearing back into the hillside.
Because this land had already been built out and stripped of its original habitat, Midpen designated it primarily for recreation once the quarantine-era buildings were cleared. That decision is why Pulgas Ridge has a dedicated 17.5-acre off-leash area today, reachable from the Cordilleras Trail, the Polly Geraci and Hassler trails, and the Blue Oak Trail. Do the math on that and it is a small slice of the whole preserve, under 5 percent of the 366 acres, with the rest requiring a leash. But it is enough that Pulgas Ridge has become the default answer in San Carlos to "where can I actually let the dog off leash without driving to the coast."
The preserve's six miles of trails also include the Dusky-footed Woodrat Trail and the Dick Bishop Trail, both looping through oak-covered hillside into chaparral with views toward the Santa Cruz Mountains. None of it demands technical hiking experience. Most of it is shaded enough to be tolerable on a warm afternoon, which matters more in August than it does in February.
The Grass That Would Not Grow Anywhere Else
Cross Edgewood Road and you are on different soil, literally. Edgewood County Park and Natural Preserve sits on 467 acres of serpentine grassland, a rock type left behind by ancient tectonic activity that produces soil most plants cannot tolerate. That hostility is exactly why Edgewood matters. Because ordinary grasses and aggressive non-native plants struggle there, native species that have vanished almost everywhere else on the Peninsula have held on. Edgewood supports more than 500 plant species, a dozen of which are rare or endangered.
The species most people come for is not a plant. It is the Bay checkerspot butterfly, a threatened species that depends entirely on a small, unassuming native plant called dwarf plantain. The butterfly's population crashed hard enough that in 2002, conservation biologist Stuart Weiss documented the last caterpillar at Edgewood. Scientists traced the collapse to vehicle exhaust from the 280 corridor fertilizing the soil just enough to let invasive Italian ryegrass choke out the plantain the caterpillars need to survive. Since 2005, volunteers with Friends of Edgewood have been mowing specific plots to knock back the invasive grass and give native wildflowers, and the butterfly's host plant, room to come back.
This is the actual reason dogs are banned at Edgewood. It is not about noise or mess. A working dog off leash, or even a dog on leash cutting through the wrong patch of grassland, is a real threat to a habitat that took decades of volunteer labor to partially restore. Friends of Edgewood runs free docent-led wildflower walks most weekends from early March through early June, and the preserve's Bill and Jean Lane Education Center stays open on weekend mornings if you want context before you hike.
Same Exit, Different Trail Systems
Once you understand the why, the practical differences make more sense. Edgewood is the larger preserve by both acreage and trail mileage, with roughly ten miles of trail against Pulgas Ridge's six, including the Clarkia, Sunset, Serpentine, Franciscan, and Ridgeview trails looping around Edgewood's 875-foot ridge. But Edgewood's popularity during spring bloom means its lots fill fast, and there is no off-leash option anywhere on the property.
Pulgas Ridge, by contrast, has a modest main lot off Edmonds Road with 23 spaces and 2 dedicated ADA spots. It fills up too on a nice Saturday, but the preserve rewards a shorter visit better. If you only have 45 minutes, the Blue Oak and Polly Geraci loop covers about 2.4 miles at an easy grade, and you can let the dog run in the off-leash section on the way back to the car.
If you want a longer, more strenuous route without leaving San Carlos's immediate hills, the Dream Trail loop at Pulgas Ridge runs closer to six miles and takes most hikers over two and a half hours. Edgewood's equivalent, the loop combining Serpentine, Sylvan, Edgewood, and Sunset trails, covers about 3.7 miles and stays moderate rather than strenuous, better suited to an evening walk than a workout.
The New Wide Path at Pulgas Ridge's Front Door
Something changed at Pulgas Ridge in the past year that most regular visitors have noticed without knowing the reason. The wide, smooth-surfaced stretch of the Cordilleras Trail near the parking lot did not always look like that. Midpen spent the past several months completing an ADA Barrier Removal Project at the preserve, regrading and resurfacing the easy-access portion of the Cordilleras Trail with Granitecrete, a material that reads like natural hardpack but holds up like pavement. The project also added accessible parking spots and graded paths from the lot to the trailhead.
Practically, that means the first 0.8 miles of trail out to the bench at Cordilleras Creek is now walkable with a wheelchair, a stroller, or a set of aging knees that used to skip Pulgas Ridge for exactly that reason. Past that point, the trail splits and the route toward the top climbs a grade steep enough that Midpen itself flags it as likely too steep for wheelchair use, so the easy-access improvement is real but bounded. Still, for a preserve that used to require a certain baseline fitness just to reach the dog area, that is a meaningful change for the residents who live closest to it.
When the Hills Are Too Far
Some days you do not want to drive to Edmonds Road or Cañada Road at all. San Carlos has its own in-town alternative sitting right in the Cordes neighborhood: Arguello Park, off Wellington Drive. It is a smaller commitment, a 0.9-mile loop trail winding through the hillsides on three of the park's four borders, with about 180 feet of elevation gain and a route that circles the property's grass field and baseball diamond. There is a bridge crossing a creek bed and the remains of a waterfall that no longer runs, along with two picnic areas locals split into the sunny site and the shady one depending on the season. Dogs are welcome on leash. Coyote sightings are common enough that regulars mention it without much drama.
It will not replace a real hike, and nobody pretends it will. But on a weeknight when the choice is Arguello Park or nothing, it is the option that actually gets used.
The Knowledge That Comes With Time Here
None of this shows up on a trail app's five-star rating. AllTrails will tell you Pulgas Ridge has good parking and Edgewood has good views, and both of those things are true. What takes longer to pick up is why the rules differ, and once you know it, the two preserves stop feeling like interchangeable options and start feeling like two different pieces of local history you happen to live next to. One used to be a quarantine ward and is now the place half the neighborhood takes its dogs. The other is holding onto a butterfly that nearly disappeared from the entire Bay Area, one mowed plot of grass at a time.
That is the kind of detail that only shows up after enough seasons of actually walking these hills, which is more or less how I think about this neighborhood generally. If you are curious about the specific pockets of San Carlos near these trails, from the Cordes streets around Arguello Park up into the White Oaks and Alder Manor hillsides, I am always glad to talk through what it is actually like to live there. Reach out through Bob Bredel any time, or just call Bob.
