The Gardens at Lake Merritt are building a rock garden in the heart of the grounds. They have plenty of gardens with stones in them already, but this will be a proper rockery. This post is about the work in progress. I know almost nothing about the plants they’ll be featuring, but I do know a little about rocks.
As we enter yet another year of drought, it’s important to note that rock gardens are made to conserve water. The stones and gravel offer solid shade to the underlying soil, and the typical plantings are small, hardy species from alpine or desert settings. As you bend down to admire these plants, have a look at the stones.
The location is between the community plots and the Torii gate, the crossroads of our remarkable garden complex. Just across the path is the hill-and-pond garden, where the turtles hang out.
This view toward the lake shows the layout. In the background is the entry to the Sensory Garden, which has had a thorough going-over during the shutdown.
The foreground containers in both photos showcase rounded river stones, blue-green argillite most likely from the northern Coast Range. I would not be surprised if some of the rock nuts of the Suiseki Societies of Northern California contributed to this project.
The center of the garden is a mound of sandstone tablets, with some accent stones, oriented north-south for optimal sun. Rings of different colored gravel surround it. Note the “do not climb” sign.
Some of the basins echo the brown sandstone of the central mound, offering textural contrast.
Others contrast more strongly. Here rough greenstone is set in crushed marble.
And what would a Northern California rock garden be without some red chert?
All of these rock types are typical of the Franciscan Complex, a lithological scrapple that makes up the bulk of the northern Coast Range, including San Francisco and the hill that Piedmont sits on. Get to know them, and you’ll see them all over the place.
The Gardens at Lake Merritt have several sectors that artfully mix plants and stones. The water garden I mentioned earlier is one, and there’s the cactus garden and the bonsai garden (which has just added a suiseki section) and the enclosed Japanese garden by the Community Center building. They’re all looking great right now, but check the hours before you go; weekends are still closed.
A few years back I wrote about the remarkable rock garden assembled by Ruth Asawa in San Francisco. As the world reopens, I hope to visit it again.
Oakland Geology 
31 March 2021 at 2:40 pm
Nice article ! Yes, some of the stones they used were prospected on a collecting trip to my yard 😉. I’m curious about the stone material identification. We suiseki people learned our nomenclature for the types of material we collection from the rockhounds who collect in the same locations. The smooth, heavy, green/blue material typically comes from places such as Clear Creek, or the Eel around Dos Rios, and I had always heard referred to as serpentine (i.e. serpentinite) with sometimes “jade” components. I had always understood it was part of the ophiolite (and how much and what kind of jade depends on how deep in the trench it got). I have not given any of it the scratch test, but it is very solid material, and the description I read of argillite seems very, very different?
The red/yellow (and black and purple) stuff from places like Stony Creek near Orland (and also Cache Creek closer to home) is usually referred to by the rockhounds as “jasper” and I’ve had the devil’s own time trying to figure out how that differs from “chert”. It’s very hard and well rounded. But seems to be formed from hot, mineral-laden water metamorphosing sedimentary rock. Can you enlighten?