Merritt Canyon

27 September 2021

Like all true Oaklanders, I keep coming back to Lake Merritt. In this visit, I’ll muse about the many times in the recent geologic past when there was no Lake Merritt here.

If we assume, as I do, that the uplifted block of bedrock making up most of Lake Merritt’s watershed is about 1 million years old, then this little arm of the Bay has a fairly deep ice age history. A million years rather neatly fits the period of Pleistocene time after the Mid-Pleistocene Transition, when for imperfectly understood reasons glacial cycles changed from roughly 40,000 years to 100,000 years in length.

Let us then stipulate that this part of town has gone through about ten full glacial cycles. Each time the world’s ice sheets and ice caps grew, the sea level fell by a hundred meters or so — three or four hundred feet! Here’s a recently published set of sea level data for the last nine cycles. Various lines of evidence agree, though never in exact detail, about the timing and magnitude of the changes. That’s what paleoclimate science looks like.


From Rachel Spratt & Lorraine Lisiecki, 2016, A Late Pleistocene sea level stack, Clim Past 12(4)

Each time the sea fell, all of San Francisco Bay slowly drained dry and the coastline withdrew out past the Farallon Islands. Every stream that could do so cut into the newly exposed ground, digging gulches, ravines and canyons into the young sediment where before they were prevented by the high sea level. That’s when Lake Merritt became temporarily Merritt Canyon, with Merritt Creek surging along its bottom.

Each time, Merritt Creek dug out all the gravel and mud that had filled the basin of Lake Merritt and shoved it straight out into the Bay, where the drainage ran south and then around the end of San Bruno Mountain into the Pacific. That’s right — the Golden Gate didn’t exist. Instead, the Bay area streams and the great Central Valley rivers drained through what’s called the Colma Gap.

Here’s an illustration from a publication I refer to often, Sandy Figuers’ “Groundwater study and water supply history of the East Bay Plain,” that shows the typical drainage pattern of those times.


Courtesy State Water Resources Control Board

It’s very interesting: the river ran east of the Potrero Hills in Richmond, east of Yerba Buena Island, and all the way down to around San Mateo. And Merritt Creek, right in the center of that map, pushed a big fan of alluvium — river gravel and sand — into the basin that rivaled the fans of the other major East Bay streams. It went right under Alameda. That’s because Alameda wasn’t there.

This configuration of the Bay lasted from about 630,000 years ago, when the great freshwater Lake Clyde that once filled the Central Valley broke through the hills and cut Carquinez Strait, until the last warm interglacial period about 125,000 years ago. The sea at that time rose even higher than it is today, and motion on the San Andreas fault closed the Colma Gap. That’s when another gap opened up farther north on the fault, which became the Golden Gate.

So when the next glacial age began, the whole drainage pattern of the Bay shifted dramatically. Also the winds: instead of blowing south through the Colma Gap, the ice age westerlies carried huge amounts of glacial sand through the Golden Gate and across San Francisco, across the dry grasslands of the Bay and onto the East Bay slopes. That’s when the big fields of sand dunes accumulated in San Francisco and in three places on this side of the Bay: in downtown Oakland, in Alameda and on Bay Farm Island.

The latest time that Merritt Canyon formed, Alameda sat in its way all of a sudden, and I think Merritt Creek must have drained west, down San Antonio Creek (today’s harbor estuary), not southward as shown on this figure from the same report.

Here’s part of a third figure from that report, showing the depth to bedrock in Oakland as determined in boreholes.

Merritt Canyon really stands out underground: over repeated ice-age cycles, as the Bay floor has gradually subsided, the earliest versions of the canyon now lie 600 feet below Lake Merritt.

There should be a record of successive incisions and fillings of the canyon preserved down there. It would take a concerted campaign of core drilling and seismic reflection profiling to map and characterize it, and if I were a billionaire like some people I won’t mention, I’d spend the money even though it would be a huge hassle to get the permits.

Posted in Oakland streams and water | 1 Comment »

Reichert’s pit, the Fruit Vale White Cement Gravel Quarry

13 September 2021

Starting on 8 June 1871, an ad in the Oakland Daily Transcript touted “White Quartz Gravel / for Sidewalks, Garden Walks, and Carriage Drives, It Makes A Beautiful And Solid Walk!” and offered this recommendation:

“Mayor N. W. Spaulding, in his recent message to the City Council, said: ‘The only macadam walks which have so far proved successful have been made from [the Fowler quarry or] the white cement gravel found in the vicinity of Fruit Vale. The latter appears to be preferable because it becomes more solidified than any other material heretofore used, being less affected by the agencies of the weather. It has been used in some localities in this city for the last eighteen months. The peculiarities which recommend this cement gravel are: that when it is exposed to the elements it becomes adhesive and firm, is comparatively free from mud in Winter and dust in Summer. This makes it a complete and permanent improvement. Sidewalks made from this material are estimated to cost about 35 cents per lineal foot for walks eighteen feet wide.’ The subscriber has now got his road through to the White Cement Gravel Quarry, and will furnish at short notice any amount of Gravel for the above purposes, by leaving orders at Gardiner & Hunt’s office, Broadway, between Eighth and Ninth Sts., Oakland, and at the Brooklyn Postoffice.”

It was signed “L. Reichert, Fruit Vale.”

This material seems quite out of place for Oakland, and its properties appear unlikely too. But I’ve tracked it to land that Reichert owned above the Dimond district, at the end of today’s Maple Avenue, where a “gravel bank” is noted on the 1878 Thompson & West map.

And we’ve been here! It’s in the land south of the LDS Temple that was ruined by the London Road landslide in 1970. And that explains the peculiarities of the material. It was fault gouge: bedrock crunched into powder by the Hayward fault.

I believe its self-cementing character comes from a significant content of calcium carbonate, which is present both in the Franciscan melange on the downhill side and in the serpentinite a little ways uphill.

Despite the mayor’s endorsement, business for the Fruit Vale Quartz Company seemed to be spotty. Business broker Andrew Baird, of San Francisco, took over for a short time in 1873 under his own name; then Reichert sold the “inexhaustible” gravel pit, and the 25-acre parcel it sat on, in July 1873 to Elias L. Beard, a prominent wheeler-dealer based in Mission San Jose. Beard is shown as the owner in later maps (misspelled Baird, probably because the adjoining parcel was owned by Julia C. Baird). The 1874 city directory lists L. Reichert Jr. as a teamster with the Fruit Vale Quartz Company — perhaps the founder’s son.

Baird tried again to sell the parcel in 1875, 1876 and 1878, the year that Beard went bankrupt and lost almost everything.

I have little idea what happened after that, except that the State Bureau of Mines annual report 38, published in 1906, recorded this as the “Packard Quarry,” of which the newspapers make no mention. And as of 1912, the land was in the hands of the Realty Syndicate, part of its enormous hillside empire. A decade later the land began to undergo the process of residential subdivision that endures to this day.

Posted in Quarries and mines, The Hayward fault | 3 Comments »

Upper Castle Canyon

30 August 2021

Sausal Creek is formed by the junction of three streams, two of which are well known: Shephard Creek, which drains Shepherd Canyon, and Palo Seco Creek, which drains the bulk of Joaquin Miller Park. In between them is Cobbledick Creek and its steep-walled watershed, hidden green heart of the Piedmont Pines neighborhood.


Source: Alameda County Flood Control and Water Conservation District

The creek has two branches: the northern one, which I’ll call Beaconsfield Creek after Beaconsfield Canyon at its head, and the eastern one, Castle Creek, which drains Castle Canyon. The easternmost portion of Castle Canyon, a gorge running from the hairpin turn on Mastlands Road, is an 8-acre preserve that’s formally part of Joaquin Miller Park. Over the weekend, that parcel was renamed Dick Spees Canyon, with a bench and plaque, to honor the longtime politician and activist who helped keep the land undeveloped.

The interesting thing about Dick Spees Canyon, and the valley of Cobbledick Creek below it, is that it coincides with the inactive Chabot fault, a deep feature of the East Bay that runs roughly parallel to the Hayward fault. It runs diagonally across this digital elevation model of the area; Dick Spees Canyon is right in the center.


From nationalmap.gov

And the bedrock map of the same area is here. The Chabot fault is the dashed line with the pairs of tick marks on the right-hand (downthrown) side.

The Chabot fault juxtaposes two very different rock units directly across the canyon from each other — the serpentine rock of the Coast Range ophiolite (sp) on the west and the Joaquin Miller Formation (Kjm) of the Great Valley Sequence on the east. Dick Spees Canyon aligns very nicely with the upper part of Palo Seco Creek, forming an unusually good topographic expression of this obscure fault. Leona Canyon is another place it stands out; also in upper Knowland Park. The fault has been traced past Hayward. While it appears to have a long history, it’s very much inactive.

The fault is why I made a point of visiting here in 2019 and returned last Thursday. The parcel is almost completely undeveloped; only a rough footpath runs up the narrow valley floor from a short formerly graded stretch, then zigs up to Castle Drive. (I must advise all visitors not to try walking it downhill until the rainy season firms up the soil there.) The following photos are from both visits.

Here’s the lower end of the property. It’s a steady climb.

Soon the rocks make themselves evident, serpentinite on the right . . .

. . . and mudstone on the left.

Whoever built this fire ring used stones from both sides of the fault.

The valley floor is littered with dead cedar and eucalyptus trunks that need clearing out. And all sides of the canyon are very steep. I don’t expect anyone to cut any trails up them for a long time.

But if they do, visitors might glimpse the views enjoyed by the ridgetop residents who surround this neglected gulch with its interesting geology.

Posted in Oakland sandstone/shale, Oakland serpentinite, Sausal Creek watershed | 3 Comments »

Mountains and other awesome things

16 August 2021

As you may know, there is no spot in California that’s out of sight of mountains. I took a long train trip over the weekend, when I wrote this post. Passed mountains the whole way until Nebraska. Now Nebraska is full of geological interest, but it is . . . subdued. It may be the largest state without mountains — no, Kansas is a little larger.

In the interest of taking a break and to practice working in a new image-editing application (Photoshop Elements, now that Paint Shop Pro 9 no longer works with Windows), I’m going to wander off the range and feature some mountains and other awesome features, starting in California — actually, starting with two of the photos I keep on my phone. I don’t believe I’ve shown them on this blog before.

Here’s Gudde Ridge and Round Top, just over the hills from Oakland. They’re honorary mountains, using 600 meters/2000 feet as the cutoff.

And here’s Las Trampas Ridge on the left and Rocky Ridge on the right, west of Danville/San Ramon. Rocky Ridge is just over 2000 feet.

And now let’s go for awesome.

I’ve tried several times over the years to capture this sight on camera: the Kern River canyon exiting the Sierra Nevada east of Bakersfield. In my opinion it’s California’s most dramatic water gap, made as a strong mountain river cut through a rising range. The Golden Gate might outdo it in geographic importance, but that’s a drowned water gap at the moment, with its lower hundred meters covered by the sea.

And here’s another awesome thing: the White Mountains, as seen in the bristlecone pine preserve.

The White Mountains are white in this area because they consist of dolomite marble. How that happens is still imperfectly understood. But what matters here is that dolomite, which resists rainwater much more than its more common cousin calcite, creates a very stable setting for the extremely old bristlecone pines, some of which are approaching five thousand years of age. It’s remarkable stuff to pick up and stare at, just as much as the trees.

And finally here are two photos from Colorado, which I rode through on Saturday. First is an image from five years ago in the mountains north of Red Rocks, showing the classic sandstone of the Fountain Formation that gives the area its name.

And here’s an image from Saturday, taken from the California Zephyr as it approached upper Rube Canyon.

What an audacious feat it was to push a railroad through here, and what an experience it was to ride through it.

Posted in Oakland rock types | 6 Comments »

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