San Mateo County Birding Guide by Sequoia Audubon Society - Printed on October 30, 2026
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You've all seen the sign from the airport proclaiming "South San Francisco: The Industrial City." Sign Hill is a geological outlier from San Bruno Mountain, separated from the south slope of the mountain by Sister Cities/Hillside Blvd. Sign Hill's summit is 581 ft. All five paths to the top are steep. The route recommended in this link is a good way to see a lot of habitats, as is an approach from Ridgeview Court, where there is a small parking lot. Behind a locked gate, a paved road for city and water department trucks climbs straight to the summit. Paralleling the road is a small wood of young conifers and scrub, bordered by a dense row of mature trees, which screen the adjacent neighborhood to the east. We often walk up the hill through this sparse planting. Birds seen here have included Golden-Crowned Sparrow, European Starling, Dark-eyed Junco, Chestnut-backed Chickadee, Ruby-Crowned Kinglet, Townsend's Warbler, Northern Flicker, and Red-breasted and Pygmy Nuthatches.
As you approach the summit, there is a large conifer forest on the right (south) which was planted by Alphonse Seubert in the 1960's (see links below). Birds in here include Steller's Jay and Northern Flicker. Uphill to the left is a water tank. It used to leak a little at the base, and the water attracted many birds, but the leak has been fixed.
Hike to the summit, where the city's electric Christmas Tree lights up every December, from which there are fabulous views north, east, and south. From this point, you can take one of three trails: the Letters Trail, the Iris Hill Trail, and the continuation of the Ridge Trail. We do not recommend going down the Iris Hill Trail unless you have young knees.
For a short hike, take the Letters Trail down to the south park entrance. Along this trail we have seen House Finch, American and Lesser Goldfinch, Red-tailed Hawk and Downy Woodpecker. In the eucalyptus grove at the bottom of the hill, we have seen breeding Bullock's Orioles. Take the Seubert Trail and the Eucalyptus Loop (Hairy Woodpecker), arriving back at the level of the water tank.
For a medium hike, take the Letters Trail, the Seubert Trail, the Eucalyptus Loop, and the Iris Hill Trail (Anna's and Allen's Hummingbird, Lesser Goldfinch, Spotted Towhee, flyover Caspian Tern) back to the summit, then go back down to the parking lot.
For a long hike, continue downhill on the Ridge Trail. At street level, hook a tight right back into the park on an unofficial trail that runs along the culvert at the base of the hill, back to the Rocca entrance. From there, take Iris Hill back to the top, or the Seubert Trail back to the water tank. The Iris Hill Trail is steep with uneven steps, but the Seubert Trail is a graveled switchback that is tedious to climb.
This park is famous as habitat for the endangered Mission Blue Butterfly. For birders who are also interested in butterflies, this is draw enough for this park. But for all visitors, this rarity provides a good reason to always stay on trail. There are often butterfly walks in spring, sometimes sponsored by San Bruno Mountain Watch. Similarly, the California Native Plant Society hosts hikes here to see the incredible spring wildflower displays.
Canada Goose, Mallard, Double-crested Cormorant (fly-over), Turkey Vulture, Osprey, White-tailed Kite, Northern Harrier, Sharp-shinned Hawk, Cooper's Hawk, Red-shouldered Hawk, Red-tailed Hawk, Barn Owl, Great Horned Owl, Western Gull, California Gull, Caspian Tern, Rock Pigeon, Band-tailed Pigeon, Eurasian-Collared Dove, Mourning Dove, White-throated Swift, Anna's Hummingbird, Allen's Hummingbird, Acorn Woodpecker, Red-breasted Sapsucker, Nuttall's Woodpecker, Downy Woodpecker, Hairy Woodpecker, Northern Flicker, American Kestrel, Peregrine Falcon, Western Wood-Pewee, Pacific-slope Flycatcher, Black Phoebe, Say's Phoebe, Hutton's Vireo, Cassin's Vireo (migration), Warbling Vireo, Steller's Jay, Western Scrub-Jay, American Crow, Common Raven, Chestnut-backed Chickadee, Violet-green Swallow, Barn Swallow, Bushtit, Wrentit, Red-breasted Nuthatch, Pygmy Nuthatch, Brown Creeper, Blue-gray Gnatcatcher, House Wren, Pacific Wren, Bewick's Wren, Golden-crowned Kinglet, Ruby-crowned Kinglet, Western Bluebird (unusual), Hermit Thrush, American Robin, Northern Mockingbird, European Starling, Cedar Waxwing, Orange-crowned Warbler, Yellow Warbler (migrant), Yellow-rumped Warbler, Townsend's Warbler, Hermit Warbler (migrant), Wilson's Warbler, Spotted Towhee, California Towhee, Fox Sparrow, Song Sparrow, White-crowned Sparrow, Golden-crowned Sparrow (fall-spring), Dark-eyed Junco, Western Tanager, Black-headed Grosbeak, Lazuli Bunting (migrant), Western Meadowlark, Brewer's Blackbird, Brown-headed Cowbird, Hooded Oriole, Bullock's Oriole, House Finch, Purple Finch, Pine Siskin, Lesser Goldfinch, American Goldfinch, House Sparrow
In this guide, "rarities" are defined as those species given an County Abundance Code of 4, 5, or 6.
Black-chinned Hummingbird (2014), Rufous Hummingbird (2017), Broad-winged Hawk (2018), White-throated Sparrow
From 101 north or south, take exit 425B, Oyster Point Blvd.
From the south, take the farthest left lane, turn, take the 2nd left lane, turn, go straight across South Airport Blvd., and you will be going uphill on Sister Cities Blvd. Halfway up the name changes to Hillside. At the top of the hill is a stop sign. Just past the stop sign is Stonegate Dr. Turn left here, then follow the road around to the left. At the top is a small parking lot.
From the north, take exit 425B and turn left at the light, moving into the right lane. At Sister Cities Blvd., turn right and follow the directions above.
From the north on 280, exit at Westborough, exit 45. Turn left at the light, follow Westborough to El Camino. The name changes to Chestnut Avenue. Continue uphill to the tee junction at Hillside. Turn right, then right again on Stonegate, then follow the road around to the left. At the top is a small parking lot.
From the south on 280, take the Avalon exit, 44. Go forward on Junipero Serra Blvd. to Chestnut, then follow the above directions.
none
accessible 24/7
The trails are steep both up and down. The lower part of the Letters Trail is covered with eucalyptus pods which roll easily underfoot. The Seubert and Ridge Trails are graveled, which can cause skidding. The Ridge Trail has been changed by the Boy Scouts from straight down to a series of switchbacks. Poison Oak is present.
You're on your own here, folks! There are plenty of restaurants and mini-marts in South San Francisco.
This park is under the jurisdiction of the City of South San Francisco. They can be reached on weekdays during normal business hours at 650-829-3800. The official website for the park can be found here.
Sign Hill is a HotSpot in eBird, with 76 species recorded in twenty-six of forty-eight time quadrants. Data is particularly lacking for January and February. Fill it in, birders!
Sign Hill Park has a place marker in iNaturalist, but it needs more thorough coverage. The importance of this site for butterflies demands it!
Author: Laurie Graham, Jeff Fairclough, Jennifer Rycenga, Uploaded: