The final chapter of Deep Oakland lastly will get us the place you might need thought Oakland’s geology begins: within the excessive hills and the rocks they expose. By now you recognize that geology — “the research of planets product of rocks” — is about tons greater than rocks and mountains, however in the long run, rocks are the place it’s at.
This chapter swings by way of the crest of the Oakland Hills from south to north, which nearly completely displays the ages of the rocks. This acquainted undulating skyline shaped solely inside the final million years or two but it surely exposes rocks whose ages span greater than 150 million years — and the corresponding historical past of California.
However first I step again and easily regard them, with admiration for his or her magnificence and affection for his or her deeper significance: “The hills are an enviornment of competing Earth energies, tectonic forces elevating the heights and erosional forces chopping them down. They current a panorama at all times underneath building, a dynamic equilibrium that comes of perpetual interaction amongst brokers of geologic motion.”
Chief amongst these is — effectively earthquakes after all, due to the Hayward fault, however after that it’s landslides: “The hills wish to slough us off. . . . Any location within the Oakland Hills, then, can anticipate to be destroyed, sooner or perhaps centuries later, by landslides and earthquakes.” The instability of this panorama didn’t matter till folks moved up there by the hundreds, beginning a century in the past as widespread automotive possession made it inhabitable.
For his or her sake I add a brief primer on the topic.
Earlier than I introduce the rocks themselves, I lay out how they match the larger image, which is that this: for a very long time (even to geologists), California was the location of a basic subduction zone, a vital a part of plate tectonics. California is particular to geologists as a result of that historical subduction zone was interrupted and damaged aside, exposing a number of totally different items that helped us first perceive subduction in depth. Oakland is a microcosm of the Coast Vary in that its rocks symbolize every of the separate elements of the previous subduction zone.
With that I take readers by way of the slices of rock within the hills that arose from subduction and its breakup. All of them are abundantly represented right here within the weblog, and in reality the endnotes of the e-book level to those posts: the Knoxville Formation . . .
the Oakland Conglomerate . . .
the serpentinite belt . . .
the Redwood Canyon Formation . . .
and the placing chert of the Claremont Shale.
I sum it multi function sentence: “Our excessive hills expose snapshots from all of Oakland’s geohistorical tales, from the subduction zone’s rock manufacturing facility to the later transpression that broke, chewed and smeared all of it sideways—topped with actual dwell volcanoes.”
The issues I’ve talked about all through Deep Oakland are associated not simply to geology however to historical past, coverage and justice. In penning this e-book I’ve tried equally exhausting to make clear the science of the altering world and deepen Oaklanders’ understanding of ourselves. “Oakland is only one place in a large world, however one exceptionally wealthy in proof of deep Earth historical past, deep Earth processes and deep human modifications. . . . This complicated metropolis has grown on complicated floor.”
