Northside knockers

I made a brief reconnaissance of the land just north of Mountain View Cemetery last week and captured a few more knockers. Poison oak is abundant here, I should report. It’s a lovely thing to see pristine outcrops, although the geologist in me wished for a handy rock hammer. In its absence, I can only say that this and the next knocker looked like typical sandstone or greenstone from the Franciscan mélange making up the area.

This next knocker is definitely chert of the high-grade type found elsewhere in Upper Rockridge. Notice that it supports less vegetation, being poorer in nutrients.

My reconnaissance was brief because the area is undergoing development, and while I didn’t notice a no-trespassing sign where I passed the fence I felt the need for discretion. The best knocker of the area, unfortunately, is under attack (click full size):

The upper body of red chert is still living bedrock while the nearer pile is loose pieces of it. I don’t know what is being planned for the area, but the chert would look nice in a fairway, or left in shabby gentility like some of its siblings.

Knocker 7

This is the last knocker I’ve documented in Mountain View Cemetery. It’s by the second road down from the one leading to the top, on the uphill side. It looks like the gray sandstone that makes up much of the Franciscan Complex.

The bulk of the upper cemetery is underlain by Franciscan mélange, a mix of rock types in a weak, shaly matrix. You never see the matrix except temporarily in roadcuts; it quickly crumbles into soil and becomes covered with vegetation. The chunks of other rock types emerge from this soil, and that’s what knockers are.

There are other exposures of bedrock along some of the cemetery roads, but I don’t count them as knockers. And there are several knockers in the off-limits land at the very top of the cemetery. Maybe I’ll document some of them next. And I really should do one more concerted search to see if I’ve missed any.

The big set of knockers, Mountain View Cemetery

Just below the highest hill in the cemetery, across a flat space south of the utility yard, is the best bedrock outcrop in the whole Mountain View property. This shot is from the south end looking toward the utility yard; red chert is in the foreground and other Franciscan rocks lie behind. I suspect that it was once a free-standing ridge that has been filled in on the east (uphill) side. The west side is a wall of trees, some of them growing right out of the rock, that hides everything pretty well.

Rocks of the Franciscan Complex, to remind everyone, include red chert, light-gray coarse-grained sandstone, dark shale, and dark volcanic rocks with various degrees of metamorphism. The volcanic rocks came first, formed at a deep-sea spreading ridge. Deep-sea ooze made of siliceous microfossils settled on the volcanics and became the chert. As the whole seafloor assemblage approached North America, sediment from the continent cascaded down submarine canyons and later turned to sandstone and shale.

All of these entered a tectonic subduction zone, marked by a deep-sea trench like those off Japan today, and the whole assemblage was squeezed, heat-treated, crumpled and plastered against the prow of the North American continent. The different rock types, ranging in age between about 150 million and 60 million years (Jurassic to Paleogene), were churned into an intricate mixture called mélange. Chunks of the harder rocks float in a scaly matrix of soft shale and tend to emerge above ground as the rocks erode into soil. Those chunks, not quite bedrock and not quite boulders, are what generations of California geologists have called “knockers.”

Later, sideways movements along the wide San Andreas fault complex tore up and rearranged this complex of rocks even further. Today Franciscan mélange is found in the Coast Range from south of San Luis Obispo all the way up to Cape Mendocino.

The top knocker of Mountain View Cemetery

Up at the very top of the public part of Mountain View Cemetery is this knocker. I think it has a mixture of rock types in it, but I haven’t lain down on it with my magnifier to tease them out. For now let’s call it greenstone, which is how the area is mapped. The stone is a bit dirty, unlike every other knocker in the yard. The groundskeepers ought to give it a good scrubbing with a water jet.

Across the road from here the other week, I passed a pile of rock and soil from a grave excavation and fingered a few of the stones—looked like a gray basalt. Greenstone is a mildly metamorphosed basalt; it often has wiggly veins of carbonate. See three examples starting here. It is somewhere between about 160 and 70 million years old, that is, Jurassic to Cretaceous.

The view of the bay and the city from up here is fantastic. The view of the hills has potential. The cemetery is slowly getting rid of the eucalyptus along the east side, and more and more of the lush hills and neighborhoods is visible every year.

North knocker, Mountain View Cemetery

Continuing my inventory of the knockers of Mountain View, this is on the far north end of the cemetery, along the lowest of the three roads back there. It appears to be the coarse, tough sandstone—technically a metagraywacke—that makes up the majority of the Piedmont block. I can’t always tell what a rock is at the cemetery because I can’t whack it with my hammer. Don’t you try that either.

The high knocker, Mountain View Cemetery

This knocker can be hard to find. It’s two roads up from Millionaires’ Row and to the south, but its bay-facing side is obscured by trees. I took this photo in 2003; today I could barely see it from the road, and I knew where to look. It’s mostly chert. I’m calling it the high knocker because it’s the tallest one in the cemetery; at least two others are higher on the hill.

If you approach this rock, beware of poison oak.

Knocker on display

Mountain View Cemetery is a manicured showcase of the lower Oakland Hills. When Frederick Law Olmsted designed it he left the natural contours of the land, and to this day it’s the nearest thing to the original oak-dotted grasslands that the first visitors saw (although the abundant elk and grizzlies are long gone). And decades before the rock worshippers of the Gilded Age put their stamp on Berkeley’s hill neighborhoods, Mountain View left the knockers alone. There are outcrops of the wild variety up near the utility yard, a couple of chert boulders in charming neglect, and there is this splendid thing left in the middle of its own circle above the Henry Cogswell monument. I should put up shots of the rest of the cemetery’s knockers—I think I have them all.