This house in Piedmont caught my eye not long ago. Homeowners who live in conspicuous places do their neighborhoods a service by making their properties shine. I appreciated the care the owners of this home displayed not just in their plantings, but also in their choice of rocks.
The site (110 Scenic Avenue) is in the middle of the block of Franciscan sandstone that underlies most of Piedmont and some adjacent parts of Oakland. The massive sandstone, of an unobtrusive tan color and undistinguished structure, makes a serviceable setting for some of the Franciscan’s other, more colorful rock types.
The exposure of bedrock is discreetly patched with concrete, which may well conceal rock bolts set into the hillside. The section of concrete on the right side, below, is surfaced with the same blue serpentinite found at Elks Peak in Mountain View Cemetery, the old pit at Serpentine Prairie, around Butters Canyon, and elsewhere.
There are several basins built onto the exposure. The bluish high-grade metamorphic river rock is carefully chosen, too. It comes from outside the Bay area, most likely somewhere on either flank of the Sacramento Valley.
And just beneath it is this little jewel of high-grade blueschist.
Of course a geologist’s first focus is on the stone. But the true beauty of a yard like this is how the rocks converse with the plants set among them over the course of a California year. I’ll be back to see that.
Oakland Geology 
11 April 2019 at 8:01 pm
Are there any buildings still standing that used the “blue rock”? I have always loved the color of those rocks. Thanks
13 April 2019 at 12:02 pm
“Blue rock” was the term quarriers used for sound Franciscan sandstone, which often has a slight bluish cast when it’s fresh, although it quickly turns a rusty color. That was rarely if ever used structurally; it was crushed for aggregate. But I think you’re referring to the blueschist. That has never been used for anything but decorative purposes.