Inkwell: Authors and Artists

    
Like David, I have nothing to add except my thanks for writing a
hugely enjoyable book!
  

    
Californians may be more literate than most about the difference
between normal and strike-slip faults like the Hayward and San
Andreas. 

But I hadn’t thought about the complex movement added by our faults
being near a subduction zone. Can you explain how that changes the
environment here? And a little bit about how we can see the
subduction zone itself in Oakland, because you mention that is
pretty rare?
  

    
Creepmeter would be a good retro nineties neoindistrial band name…
  

    
Subduction is no longer active in the Bay area, so our tectonic picture is
simpler than elsewhere like Southern California, where the San Andreas fault
system is badly bent, and California north of Cape Mendocino, where
subduction is still active (along with the Pacific Northwest). What we see
in Oakland, as we do all up and down the Coast Range, is dismembered pieces
of the former subduction zone. Starting in 1970, California geologists did
pioneering work describing and analyzing subduction zones based on those
pieces, which represent the depths as well as the breadth of a well-formed
subduction zone. Oakland is lucky in having a very representative set of
subduction-related rocks.
  

    
Say more!
  

    
Starting with the present, the San Andreas fault system extends from
the head of the Gulf of California to the Mendocino Triple Junction.
It moves at a speed of about two centimeters a year, roughly the
rate at which our fingernails grow. It's a right lateral fault,
which means that wherever you look across the fault the other side
is moving to your right.

While most of the motion we're familiar with today takes place on
the Sam Andreas Fault the fault system is made up of a number of
roughly parallel strands, including the Hayward Fault, the Calaveras
Fault, the Pilarcitos Fault, and the Pescadero Fault. This is why
when we look at a geologic map of the Bay Region we see a pattern of
northwest-trending slivers of contrasting rock types next to one
another.
  

    
At the south end the strike-slip motion grows out of the seafloor
spreading that's opening the Gulf of California. At the north end
the fault curves around until it's perpendicular to the coast, and
merges into the Mendocino Fracture Zone within the Pacific Plate, a
scar in the Pacific Plate that has had faster seafloor spreading on
one side than on the other.

There's a big S-curve in the fault in Southern California, from
about the latitude of Santa Maria down to San Bernardino. Because
the fault motion isn't parallel to the trend of the fault the two
sides of the fault push against each other, and push up mountain
ranges: the San Bernardino Mountains, the San Gabriel Mountains, the
Transverse Ranges.

Where the fault is more or less straight the two sides of the fault
still press against one another because the motion of the Pacific
Plate isn't quite parallel to the motion of the North American
Plate. This pressure pushes up the Coast Ranges and propels small
faults, some of them strike-slip and some of them thrust faults.
  

    
Mary, the textbook subduction zone consists of an oceanic plate plunging
beneath another plate (which can be oceanic or continental). The west side
of South America is a good analog of what California looked like through the
entire Cretaceous Period and well into the Cenozoic Era that followed (and
in which we live today). Where the two plates meet is a deep-sea trench
running offshore. As the descending plate encounters more heat and pressure,
it releases most of the water it contains. This water triggers melting in
and beneath the overriding plate, and ta-dah you have a long line of
volcanoes. Between the volcanoes and the trench is a belt of busy territory
that (1) collects a huge load of sediment eroding off the volcanoes and (2)
dumps a lot of it into the trench in landslides of all sizes -- it's called
a foreland basin. In central California the volcanic chain is now the Sierra
Nevada, representing the volcanoes' deep granite roots. The foreland basin
is still around -- the Central Valley. The trench area with its slumgullion
of mixed rocks and sediments is represented by the Franciscan Complex, found
up and down the Coast Range. The Oakland Hills contain slices and packets of
Franciscan and Great Valley Sequence rocks, not to mention the oddball
ophiolite, a long slice of oceanic crust that wound up on land during the
subduction era.

You may ask, what about the Sierra Nevada granite, is there any here? I say
yes with tongue in cheek, because City Hall and many other downtown
buildings are made of it. But also, most of the sand in the sandstone and a
few of the cobbles in the conglomerate originated in the Sierra. It's all
here within and around our city boundaries.
  

    
A bit of a trivia question. You say:

Between 1840 and 1860, Americans felled every [redwood] tree but
one. The last old-growth redwood on this side of the Bay, nicknamed
"Old Survivor" and nearly five hundred years old, is in Leona
Heights on a cliff in Horseshoe Canyon. (161)

Is there a pointer for that sign, or is it best not to reveal
exactly where it is?
  

    
Frako, I’ve looked for it unsuccessfully!
  

    
Surely Andy can give us a hint or two. We wouldn't carve initials in it.
  

    
The sign is at the entrance to Carl Munck Elementary School on Campus Drive:

<https://oaklandgeology.com/2015/08/10/survivor-trees/>

The tree is well protected simply by its precarious location. In the dry
summer duff, climbing up to it is treacherous and climbing down to it is
strenuous. Taggers and carvers are gonna leave it be.

<https://localwiki.org/oakland/Old_Survivor_Redwood_Tree>
  

    
I attempted to approach it from below, up the York Trail from Leona
Heights Park (not to be confused with Leona Canyon Regional Park).
It’s what I’ve called the loneliest trail in Oakland, and it just...
stopped at one point, overgrown and with trees fallen across it.

Andrew, you talk in the book about how pyrite and ocher helped shape
the human geology of that area. I was startled to learn that fool’s
gold is not actually worthless.
  

    
I've been to some of of the super tall redwoods up north and from
ground level they don't look any different from the rest.
  

    
It all started with what everyone called the sulfur mine, up at the end of
McDonnel Avenue. I checked it out early on when I began exploring oakland
systematically. I saw the orange-stained creek bed downhill from a barren
cleft in the hillside and recognized the sign of acid runoff.

Pyrite was the basis of the sulfur industry back in the late 1800s. It would
be roasted to oxidize it (FeS2 + oxygen --> Fe oxides and SO2), and the SO2
gas was easily processed into sulfuric acid, which is kind of a skeleton key
for industrial chemistry. Today we get sulfur from other sources, but pyrite
deposits are still of interest because of the other metals besides iron that
lurk in sulfide minerals, notably copper, silver and gold. The pyrite mines
in Leona Heights did yield some copper over their lifetimes, but the gold
and silver values were too low to be worth the work of extracting them.

Old-timers have told me that the collecting was good at the former mine
sites, but I never tried myself. Oakland is the type locality for the
mineral boothite, a hydrated copper sulfate with a lovely light sky-blue
color. I wonder if some local people have pieces in their attics.
  

    
My memoryis that the creek along the York Trail is a rusty color,
but it's been a long time. 

(I also Did Not Know That pyrite and ocher were related.)
  

    
There are patches of orange here and there in Horseshoe Creek that appear to
be of natural origin. The hillside is still infested with pyrite, and the
creek cuts deep into it and undoubtedly exposes fresh rock. I think those
facts are related.

Yeah, major sulfide deposits often have an "iron cap" or gossan, formed as
the sulfur washes away and the iron oxides remain as an earthy crust. In
Oakland the gossan was thick enough to support a whole Ohlone industry. They
would dig the ocher, process it and trade it with tribes all over the Bay
area for good stuff Oakland doesn't have: salt and cinnabar from the South
Bay, obsidian from the North Bay, abalone beads from the Pacific coast, and
so on. Ocher is a pigment, offering a range of colors from sienna to umber
though bright brick red. In cultures without clothing (other than ceremonial
garments), body paint is a basic essential. I like to say that Oakland has
made every wave of its human inhabitants wealthy.
  

    
OK, I won't try to reach the Survivor Redwood. I love how being ugly and
useless saved it from being cut.

I just watched a documentary called THE COLOUR OF INK, and it spends time
talking about ochre. (I don't think it's available for watching anywhere but
film festivals right now) Trailer: <https://www.nfb.ca/film/the-colour-of-
ink/>

Short video about ancient uses of ochre:
<https://www.youtube.com/watch?v=RGpqBYB3vHc>
  

    
(I did some student archaeology under Charlie Slaymaker at Olompali
in Marin, and ocher is one of the things you look for!)
  

    
Those ancient cave paintings in Europe used it. Neanderthals used it. It's
also good for sun protection and insect discouragement.
  

    
A change of topic sparked by my receipt this morning of a
communication from the USGS (hidden in the next post).

Although virtually all of us in the city call our elevated portions
the Oakland Hills, their official name as registered with the
federal government is the Berkeley Hills — the entire range, from
San Pablo through Fremont, was named thus by some boffin at the
University.

Elsewhere on the Well, Andrew has offered gentle encouragement in my
decade-long, frankly quixotic campaign to get the official name
changed to match common usage. So OF COURSE I noticed that in DEEP
OAKLAND, they are consistently called the Oakland Hills, capital H.

Is there any sort of a geologic case that the range can be broken
into segments, and all or part of it attributed to Oakland?
  

    <hidden>
  

    
The best argument for changing an "official" name is that it
conflicts with common usage. Keep calling them the Oakland Hills,
and I will, too!
  

    
The direct answer to your specific question is that no, there is no
*geologic* case for defining the *geographic* entity formally known (by
those dastards at the U.S. Board on Geographic Names) as the "Berkeley
Hills." The geographic case is that Oaklanders outnumber Berkeleyans.

I used to sit across the hall from the late Rudy Kopf, maven of geologic
names and also a member of the Board on Geographic Names. They aren't really
dastards. Besides, they're busy right now erasing old names with derogatory
terms and finding new names, a noble project.
  

    
Trinity College has decided to rename their Berkeley Library because
the bishop was a slaveholder. Maybe the BGN would accept that argument
and rename the entire range. Let the Berkeley hill folks deal with
living in the Oakland Hills for a while.