SF is Five Stripes of Goo: Hiking for Geology

This is a little out of my typical format for my Urban Hike series, in that it’s spent documenting two whole Saturdays hiking various points around San Francisco instead of highlighting one particular hike. Some of these will doubtless turn into future Urban Hike posts of their own right, but for now I really just want to share the pix from two fabulous 9-hour hiking days.

The motivation was school. I took a class at CCSF called Geology of San Francisco. We have a unique geology in the world, and it’s pretty nifty to go out on a field class with an expert in the subject (Katryn Wiese, if any of y’all plan to attend in the future.) Over the past two weekends, our class has met at different sites and carpooled from spot to spot, with a good 7 hours of the day being spent hiking, digging, talking, sketching, identifying. SF has five distinct slices of terrane (a geologically specific region or component of the land), added over millions of years by the tectonic movement that created the San Andreas Fault at our feet. Each of the five diagonal slices of SF was basically scraped off of one plate onto the edge of the other, kinda like if you take apart an Oreo and bulldoze the goo with the other half – you get a broken pileup of goo. Keep going: bulldoze another flavor Oreo, and you get another stripe of goo. SF is five stripes of goo.

I’m not gonna go into all the geologic details on this garden blog, beyond what I just wrote – unless a pic warrants a bit of further explanation. This is gonna be all about the pix. 🙂

India Basin Park

Last week we started at India Basin Shoreline Park, on the southeastern waterfront of SF, along the bay. This park is landfill. Rubble piled on top of the bay mud, topped with dirt and planted. Voila! Land. Interestingly, this park has the only remaining natural contact between bay and native soil. 95% of the bay shorline has been built upon. Here there is one solitary outcrop of CA state rock Serpentinite, popping out of the Bayview hill, and reaching its fingertip to the beach.

Candlestick Point

We headed south to Candlestick. Another park built on landfill. Windy. Damn gorgeous views of the bay.

Brisbane Quarry

West of Candlestick, and a bit to the south, is San Bruno Mountain. There’s been a quarry here since the 1860’s, producing aggregate for local road construction. They also recycle old asphalt into new roads! Awesome.

San Bruno Mountain State Park

At the top we stopped to eat our packed lunches and enjoy the views. I’ve been up here before, for various other horticulturally-centered classes, and found myself enamored by the plants, more than the rocks. 🙂 So many natives thriving in this harsh environment. Rocky, shallow soil, windy as all get-out. The plants tend to be short and scrubby, clinging tight to each other and hunkering down in the wind. The generally foggy conditions make everything – everything – a living host to mosses and lichens. SO gorgeous! And we even found a rock outcrop with fully-formed quartz crystals.

Colma Sand Dunes

Just south of SF is the city of Colma. Colma has the distinction of being the cemetery city for the area. (Spell-Check wants me to change it to Coma.) If you’ve ever driven to SFO, you’ve passed through countless cemeteries. There are some living inhabitants here, too, and their homes are built upon a series of sand dunes. In one place, dunes tower four stories over the roofs of the adjacent houses, which had retaining walls to keep the yards dune-free. For now, anyway. Through every street tree opening you could see dune sand.

Big looming sand dunes towering over the houses, and all I came away with was a vial of sand and a picture of a flowering Corymbia ficifolia tree. Hmm.

San Francisco Mint

This was more of a sad visit than anything. The big chunk of rock that the US Mint sits upon is being cemented over. But with good reason. It is the California state rock, Serpentinite, which dissolves when exposed to water. Seriously, within a year the exposed surface becomes as soft as a sponge. You can literally push your finger to the knuckle into the rock, and it just dissolves. Great thing to build a huge concrete building on. So, they are now facing the surface all around with concrete. Disney-ifying the look of the rock, as it were.

No pix to show from here, since the only section of natural stone still visible is covered by chain-link fencing, in preparation for a spray-on coating of concrete. A construction crew was working right there to repair Muni streetcar tracks, though, and I scored an awesome old rusty twisted railroad tie to incorporate into our garden art at home.

Corona Heights

The big red rock above the Castro, on the hill separating Eureka Valley from the Haight-Ashbury, is Corona Heights – almost the geographic center of SF. It has a great little museum (Randall Museum), and wildlife habitat (including reported coyote sightings), besides the geologic wonder of fabulously folded radiolarian chert. Pretty, brick-red layers of stone that would have been the result of tiny organisms’ skeletons raining down on the sea floor for millions of years and compacting, then folding as that sludge scrapes off like so much Oreo goo, eventually hardening into the rocks we see today.

Telegraph Hill

Week two’s hikes started at Coit Tower, and I know for sure I will be doing a future post on the staircases over here. There are plenty of offerings out there already on the Telegraph Hill staircases, especially after Tales of the City. I’ll add my bit anyway. 🙂 On my way to meet the class, I got up the hill from Embarcadero via the Greenwich Street stairs. Beautiful views and gardens abound… The steep sides of the hill were created when mid-nineteenth century San Franciscans blasted the hill apart to use the rocks as ships’ ballast. Now it’s prime real estate. 🙂 Every bit of open space is either a private garden/yard or is common space that the neighbors maintain with equal attention to their own gardens. Quite a treat!

Fort Point

Underneath the Golden Gate Bridge in San Francisco is Fort Point. It’s a circa 1860’s brick military fortress, built to protect SF’s bay (and the wealth from the still-young Gold Rush) from the like of the Brits, the Russians (fur traders up and down this coast in the day), and the “pesky Confederates”. The Civil War broke out right when the building was finished, but new rifled artillery made brick fortifications useless. This building was the last fortress of its kind built by the US military. This part of the land, where the fortress sits and the Bridge is anchored, is also Serpentinite. Spongy, dissolvey Serpentinite.

We totally had a wave splash through the open windows of our car as we drove out there. So awesome! We stopped and caught another. Woohoo!!!

Battery Godfrey

The hillsides on both sides of the Golden Gate are riddled with old batteries and bunkers. Batteries as in cannon or gun mountings, not as in 9-volts. Godfrey is immediately west of the bridge toll plaza, and can be reached on foot from the parking lots right there at the bridge. The hills were carved up to make places for them, so the rock exposure is pretty excellent. Not to mention, the cliffs themselves are constantly being eroded by the waves and fast-moving currents through the strait below. Good, loose rubbley soil, saturated from a few days of intense rains, being undercut by the waves. Perfect place to hang out and see what geology is all about.

Fort Miley

This is waaaayyyyyy out there, the very top left corner of the City. In the woods above the Cliff House and the ruins of the Sutro Baths. Nice wide flat paved road that used to have a steam locomotive to bring 19th century San Franciscans out to the baths. Massive landslides annually eventually made the tracks all go away and the builders give up on the effort of maintaining them. Plus, cars came along, so the beach was no longer a couple hours’ journey across the dunes from San Francisco. We could see clearly where landslides had changed the lay of the land. Most excellent.

Disappointed that I somehow missed taking a single picture out there. Lame.

Grand View Park

This park was SO cool that I could easily pretend I was nowhere near the “dreaded Avenues”. Not to be disparaging of the Avenues, there’s just a general attitude in SF that the beach side of town is Suburbia. My friends and co-bloggers (and co-students and co-worker) over at Far Out Flora live at the very extreme end of the Avenues, facing out over the beach, and exemplify the beauty that gardens can achieve out there. Plus, they’ve got a beach at their doorstep. They’ve also taken on renegade gardening in their vicinity, planting plots in the median strips and such. Nice! They have singlehandedly made me appreciate the good of the Avenues. Then this park came along and rocked my world again!

Another fine chunk of twisted chert, covered in blowing sand (the Avenues would naturally be 100% sand dunes). Phenomenal views north across the strait, east to Twin Peaks, west to the Farallones Islands, south to the horizon. Amazing. Beautiful native plantings being introduced to replace the invasive ice plant that is so ubiquitous up and down our coastal dune communities. Native ferns clinging to life in a rock crevice… Native Sedum species in a quarter inch of soil… Sticky Monkey Flower planted on the slopes…

Ocean Beach and Fort Funston

We ended our second field day walking the beach southward from the zoo. Tide cut us off at a promontory, so we backtracked and relocated further south at Fort Funston to approach from the other direction. We saw some cool stuff: massive erosion collapsing the dunes that the parking lots are built on, and the associated rubble of collapsed parking lots (go geology). We saw a massive mudstone-based cliff of dunes with evidence of a volcanic eruption 400,000 years ago (the Rockland Ash layer, if you’re interested). We saw fossils by the thousands – clams and sand dollars, from a million years ago and more. Just amazing. And magnetic sand. The sands here contain lots of magnetite, which separates from the rest in the blowing wind, making cool patterns and creating black sand patches among the beige. And it sticks to magnets. And it’s sparkly. Good stuff.

Now I just have to pull some of these into more focused Urban Hikes of their own!