EarthCaches in Oakland

14 March 2022

Maybe you’ve heard of geocaching, the wayfinding sport that’s swept America since 2000. The basic game involves hiding and finding secret packages in public spaces, all of which — GPS coordinates of the hides and logging of the finds — is administered via the geocaching.com website. My first exposure to geocaching was during a 2004 outing to remote Idria, California, where my friend Jef made a stop to visit and log this ammo-box cache in a roadside boulder pile. All he knew was the latitude and longitude.

The geocache visitor may find a paper logbook inside along with various trinkets.

As with a Little Free Library, visitors may take a trinket and leave one for a future geocacher.

I did not take up this hobby until last month, when I decided to take part in the Geological Society of America’s EarthCache variant of geocaching. (I’ve been a GSA member since the 1980s.) An EarthCache is a nonintrusive, virtual geocache without a container or trinkets, just a set of coordinates attached to a little free geology lesson about that location. You find your way there, observe the scene with the help of the lesson, and log the cache by submitting the answers to a set of questions posed by the cache’s creator.

Naturally I wanted to set my EarthCaches in Oakland. My first two EarthCaches have been approved, and as of this writing the third is under review by the GSA team. [Late update — here’s the third.] The first is up in the high hills, and the second is near Montclair. If you’re a regular geocacher, go for it! (There are a half-dozen other Oakland EarthCaches besides my two.)

If you aren’t a geocacher yet, you’ll find when you follow those links that the locations are censored, but the descriptions are visible. That means you can play a reverse version of the game if you like: from the descriptions, figure out the location and post it in a comment.

If that sounds fun, here are hints for each EarthCache. These are photos that visitors have sent me to document their visit. This one is from the first EarthCache.

And this one is from the second.

For Galaxy Brain status, tell me the locations without visiting the EarthCache pages.

This is a side project that I’ve spun off the book project, which is coming along nicely.

Posted in Oakland geology puzzles | 4 Comments »

Art concrete at UC Berkeley

28 February 2022

I have occasion to walk through the UC Berkeley campus often, and there’s a lot there to see. Recently a subtle feature caught my eye at Morgan Hall, which is otherwise a pretty undistinguished building — this rich concrete screen that borders its brick courtyard.

It does a lot of work in a discreet way.

The ten panels of rugged dark concrete, identical but alternately rotated, are laid out like a Japanese folding screen. They form an effective barrier, but the visual impression is of lightness and transparency. Two small accent panels of polished colored concrete individuate each frame. Rounded benches on the inside invite a closer visit.

The eucalyptus trees in the courtyard offer organic forms that play off the surrounding hardscape, and the accent panels reward close inspection on a sunny day. They aren’t run-of-the-mill gravel. The colors are precise.

The brisk grain boundaries and crisp polished faces, one random and the other geometric, tease and please the eye.

The blends of clasts and matrix are tightly controlled.

And what is it about that dark gray framing? Look close in good light.

Not only is it sprinkled with light grains accentuating its darkness, but the dark rock is shot with color, the deep green and blue glimmer of pyroxene minerals and serpentine. A real artist made this. I wish I knew who it was.

Two women named Morgan left their mark in Berkeley. Agnes Fay Morgan (1884-1968) was a pioneering scientist in the field of nutrition who during a long career at UC Berkeley (1915-1954) rose to the head of its College of Home Economics. (The other one was Julia, the architect.) She was widely celebrated as a founder of nutritional chemistry and a person of influence. The Berkeley Chemistry Department recalls that “Dr. Morgan’s teaching was characterized by enthusiasm for her subject, clarity, and a seemingly boundless energy. She had a sublime confidence in her rightness and a genius for disregarding nonessentials and relaxing when the opportunity presented itself.” Morgan Hall, built in 1953, was renamed in her honor in 1961. I can’t help but think that Dr. Morgan indirectly influenced my own mother, who earned a Home Ec degree from Cornell University, another progressive school, in the early 1940s and put it to full use raising and nourishing six children.

Posted in Oakland stone, Other topics | 2 Comments »

Murieta Rock, El Cerrito

14 February 2022

In Gold Rush days, the Bay area was as wild as the rest of California: depopulated of Indigenous people and a free-for-all of frontier characters. One of those characters was the legendary outlaw Joaquin Murieta. His story, at least the version we have today, had all the makings of legend — a handsome, peaceable Mexican, viciously victimized along with his wife and family at the hands of Americans, who turned desperado and came to a bad end. As befits a good legend, every crime in California was added to his name — and this fine outcrop too in the hills of northern El Cerrito.

The rock stands out in early photos of El Cerrito, back when the hills were still bare, but today it’s unobtrusive in surroundings of trees and homes at the intersection of Cutting and Arlington Boulevards. It’s also smaller than it used to be; a rectangular quarry pit has been carved into its southwestern side.

Supposedly Murieta’s gang would watch the main road from up here and swoop down on victims. Or this would be their lookout when they hid out in Wildcat Canyon. That may have been. I think the name stuck because it looks like a broken-down haunted house made of a rare, unearthly-looking blueschist.

The area is geologically interesting. The rock is just south of Cutting, below the large “L” at the center (part of the name of the old San Pablo rancho).

All the bluish rocks are Franciscan, the orange (Tor) is the much younger Orinda Formation, and between them is the Hayward fault zone. “KJfy” is a metamorphosed sandstone and “spm” is the melange. Regular readers may recognize “Jsv” as the Leona volcanics, but this little pod is actually the northernmost occurrence of Northbrae rhyolite, the stuff of Berkeley’s rock parks. (Thanks to Karl in the comments for flagging my oversight.)

Murieta Rock is a high-grade block in a melange of serpentinite — a rare outcrop within a rare setting — and for background I refer you to this post from the last time I was up this way. Notice the large areas of the map labeled “Qls”; these are gigantic, slow landslides all of which originate in that melange. More of them are in north Berkeley (see my 2017 walking guide to the area, from the Berkeley Path Wanderers Association site).

Enough of that. You can reach Murieta Rock on the 7 bus line, from either the El Cerrito del Norte or Downtown Berkeley BART stations, or drive there yourself of course, but I enjoyed walking there through Canyon Trail Park — if I were Murieta, I’d swoop that way to carry out my robberies. The view from the top of the rock over San Pablo Bay is superb.

And since this is Valentines Day, why not consider the rock for a romantic geo-outing?

Posted in Franciscan rocks, Oakland blueschist | 5 Comments »

The search for Rockridge Rock, renewed

31 January 2022

This last week I decided to make new assault on a puzzle I featured here back in 2008: What was the gigantic rock that gave Rockridge its name? I’m here to declare the controversy over, no thanks to me.

A few things have changed since then. One is that I ponied up for a subscription to newspapers.com to get full access to this primary historical material, a resource not easily available to previous researchers (or me). Another is that I’ve acclimated to newspaper writing from the Yellow Journalism era and realized how much of it was blatant shilling for advertisers and not to be trusted.

People in early Oakland had no city parks, other than the handful of public squares in the downtown area (most of which are still there). But the compact young city was surrounded by farms and open fields. It was easy for those with time and cash to spare to pack a picnic basket, ride one of the horse-drawn trolley lines to the edge of town and find a lovely spot to lounge and pass the day away from the smoke, dirt, fumes and horse manure that accompanied nineteenth-century civilization. In Oakland proper, one such place was the upper valley of Temescal Creek out by the Livermore estate, north of Mountain View Cemetery. (East Oaklanders favored the valley of Laundry Farm, now known as Leona Heights.)

The Livermores relocated to San Francisco and sold their estate, which was devoured by various developers over the years as the city below expanded. The Claremont Country Club and golf course got a big part, but the higher hills stayed idle longer. Then the Laymance Real Estate Company got hold of the high ground in the late 1900s decade and laid out the lots and streets of an exclusive suburb for wealthy white men, today’s Upper Rockridge.

Laymance had to muster up as much pompous puffery as possible, and its totem was an outcropping it named Cactus Rock. Here’s its icon in the first “Rock Ridge Gazette” weekly advertising feature, printed on the back page of the Oakland Tribune in March 1910.

Read that for a taste of what I mean by “puffery.” The Gazette went through at least twenty-one numbers in this vein.

Laymance brought parties of fashionably dressed people to the site and touted “the famous old Rock Ridge picnic grounds” to suggest memories of the good old 1870s. The promotional photo of one such party, draping themselves all over Cactus Rock, became the cover image of “Rockridge,” the Arcadia Press book by Robin and Tom Wolf. It looks huge on page 46. The rock’s image also appeared on Laymance’s lavish marketing pamphlet.

Today Cactus Rock is well hidden in a back yard overlooking Acacia Drive. Without a drone or access to the property, this is the best I can do to show it. It doesn’t look huge any more, but it still is, although maybe part of its base was removed.

After years of combing the area on foot, discounting imperfectly informed sources and tempting myself with the alternative of “Mount Ararat,” it’s finally clear to me that Cactus Rock was the subject of the old photo and the inspiration for the developers. “Rockridge Rock” is probably a legend in my own mind, suggested by taking the newspapers too seriously. I think the oldtime picnickers had lots of pleasant rocks to choose from.

Note that the drawing of Cactus Rock shows a clump of what looks like prickly pear at its base. Somewhere I have read that the first Spanish residents planted cactus near landmark boulders, in the early 1800s, and that a few ancient specimens are still around. That is to say, many rocks were “cactus rocks.” I hope a reader can retrieve that factoid for us.

Posted in Oakland boulders | 8 Comments »

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