Archive for the ‘Oakland geology walks’ Category

Merriewood spur

20 March 2023

Since my previous post, I’ve gone ahead and hiked the faceted spur next to the Montclair spur. It holds the Glen Highlands and Merriewood neighborhoods, so I’ve named it the Merriewood spur because Merriewood Drive is the nicest part of the walking route.

The 1897 topo map shows the spur in its clean, original state between the narrow mouths of two wineglass valleys, Temescal and Thornhill Canyons. The Hayward fault runs diagonally through Lake Temescal.

As I detailed in my circumambulation of Temescal Canyon, this part of town has undergone a serious amount of human modification since then. But it has appreciably affected the ridge route on the spur only at its northwestern tip, as seen in the digital elevation model.

Looking at this image, I note that the spur is larger and more deeply eroded than the Montclair spur. It’s conceivable, though not at all certain, that the main incision includes a large landslide. Other than that the image reveals no great secrets.

The route around the spur is about four and a half miles. This is one version that starts and ends at the north parking lot of Lake Temescal Regional Park. The hike along the north limb of the spur follows PG&E’s major power line, and the portion on the south limb follows city streets.

Zoom in on it at

It’s a climb of about 800 feet. A shorter version could start from Montclair Village and reach the north end of the spur via Pali Court. Or you could try the version I took, going up to Broadway from the Rockridge BART station and ending in Montclair (thus qualifying as a ramble).

The rest of this post will focus on the rocks to be seen along the north limb, because unlike the Montclair spur, the Merriewood spur includes a variety of rock units, as shown on the geologic map. I can’t vouch for the accuracy of the map along the south limb, where precious little bedrock is visible in a casual walk.

Jsv, Leona Volcanics; KJfm, Franciscan melange with chert and greenstone blocks; KJk, Knoxville Formation; Kr, Redwood Canyon Formation; Ku, undivided Great Valley Sequence; Tcc, Claremont chert; Tes, Eocene mudstone; Tsm, Sobrante Formation; Tush, unnamed Miocene mudstone.

Here’s a view of the west end of the ridge from halfway up, just to the left of “Tush” on the geologic map. I was last here in November of 2008.

It shows Lake Temescal and the shutter ridge behind it, the PG&E station in front of it and the power line pad carved into the west end of the spur.

I climbed up from Broadway to the power line because the footing is pretty good at this time of year. The clean-cut slope exposes dark, crumbling shale of the Knoxville Formation. I’m excited to see this perishable stuff.

The western tip of the power line pad exposes the familiar rugged, red-stained rocks of the Leona Volcanics.

The contact between these units is important, but rarely exposed. I want to return and look for it.

Farther up the slope, the rocks change to this sandstone. The boundary between the black shale and the blond sandstone is the enigmatic, long-inactive Chabot fault, and the two rocks differ in age by about 60 million years.

The “Ku” unit lumps together a bunch of rocks that correspond to a whole set of Cretaceous rocks, the Great Valley Sequence, that farther south is divided into several different formations. It might be possible to map those units into this part of the hills, but the last person to try, Jim Case in the early 1960s, gave up.

Turning around, I spotted the same set of stones that puzzled me in 2008.

This time my accrued years of experience, plus the acid bottle I didn’t have with me the last time, told me right off that these are limestone, not native to the area (unless I and all my predecessors are badly mistaken). They look like river rocks that have been etched by exposure to our slightly acidic rainfall over the years.

Presumably PG&E brought in a truckload once upon a time for some reason. I also visited the old, deteriorating Horse Hill dirt jump and saw that it had a fresh tire track.

A little farther uphill, the roadbed displays some bedding features — offshore channel deposits, tilted nearly perpendicular.

This view looks up toward the top of the climb right at the edge of the “Ku” belt, where the soft Sobrante Formation mudstone underlies a long-lived landslide I’ve featured here before (in 2008 and 2018).

The continuing collapse of the hillside has opened a new front. Landslides don’t give up easily. The continued existence of this walking route is not guaranteed.

That’s the north limb of the Merriewood spur. Having walked it, I can now vouch for the whole circumambulation of Temescal Canyon, and maybe some day I’ll actually hike it all in one go.

This view is from the south limb, near the bottom. Thornhill Road, visible at lower left, marks the valley of Temescal (formerly Kohler) Creek.

We’re looking across the narrow mouth of Thornhill Canyon, then across the narrow valley marking the Hayward fault, then across the narrow water gap of Dimond Canyon, then across the wide San Francisco Bay basin to the Santa Cruz Mountains.

Montclair spur

6 March 2023

One of my little geological fetishes is a geographic one: circumambulations. Thanks to the Hayward fault, Oakland has acquired several wineglass valleys, with very narrow mouths and wide headwaters. I’ve pioneered hikes that circle three of them: Claremont Canyon, Temescal Canyon and Shepherd Canyon.

These are strenuous outings, and I’m getting less and less young. This year I hope to resume them, but it will take some working up to. But I had a brainstorm: what about the faceted spurs between the wineglass valleys? I’ve written about faceted spurs before, but it felt kind of obscure so let’s try again.

Here on the 1897 topo map I’ve outlined the faceted spur that overlooks Montclair, between the narrow mouths of Thornhill and Shepherd Canyons. The fault runs from the upper left corner to the middle of the bottom edge. The spur is about 700 feet high and a loop on it is about 2.5 miles, as opposed to a further gain of 300-plus feet and 4 more miles for the circumambulation.

Visualizing this topography with the digital elevation map and picturing the hills covered with grassland, the way they used to be, I’m thinking this would’ve been a picturesque hike, on ridge routes the whole way.

You can see that the spur doesn’t have the ideal flat facet — it’s been dissected somewhat into small valleys — but the ridges that make up the rim are still nice and strong. And a lot of the streets run along the rim to offer a fair approximation of that 1897 hike. Here’s the route, starting from the end of the 33 bus line; I’ve taken it both ways and I feel fitter already. If you try this, be very cautious as you walk along Colton Boulevard.

Zoom in on the route at

The triangle of streets inside this loop isn’t part of either Thornhill Canyon on the north or Shepherd Canyon on the south; you might call it pure Montclair. It faces southwest, and as you climb you begin to peek over the Piedmont crustal block toward the Golden Gate. This view is from the north end, where the ridge runs east-west . . .

and this one is from the south end, where the ridge runs north-south.

On this ridge too, Asilomar and Drake Drives offer open views over the mouth of Shepherd Canyon toward the South Bay.

Note a couple of things in this view. The notch behind the tree in the middle is where the San Andreas fault runs as well as Route 17 to Santa Cruz. The LDS temple to its right is where the Hayward fault runs, continuing right through Montclair along the freeway. The little valley that holds Montclair owes its existence to the fault, which grinds the rocks to an easily erodible state. Elsewhere along the route, you can look north along this valley, as here at the northernmost end of the Montclair Railroad Trail.

The two ridges meet just above the Forestland Reservoir, which is a nice quiet place to have a sit before starting down — or heading farther up the main ridge to the wonders of Skyline.

The rocks along the way are all pretty much the same: medium-grained sandstone of the Redwood Canyon Formation. The south end of the loop is mapped as the Shephard Creek Formation — sandstone plus shale — but you won’t see any of it.

I have no great insights or cool things to note about these rocks. Like I said, walks like this are a geographic fetish.

The geo-flaneur

26 December 2022

I’ve always been a walker. As a child I was prone to wandering off; as a teen I learned that if I walked long enough I’d arrive in another town. My legs take my head to a special place. Since moving to Oakland, more than thirty years ago, I’ve gradually transformed into a flaneur: someone who enjoys just strolling around my city, or any city, no particular place to go, free to “lean and loaf at my ease, observing a spear of summer grass.” I love to revisit Oakland’s places and watch them change along with me.

My special joy and erudition centers on our special geology. The more I see of it, the more it speaks to me. Some times it even shouts. This blog began with an urge to share what I was perceiving, and it nurtured a private dream that the urge might somehow evolve into a book. The work involved was daunting; it started late and took years of one step at a time. It was not something a flaneur would do. But last week the final text was sent to the printer, and the publisher has a page with preliminary reviews.

One of those reviewers, our own Jenny Odell, says the book “has turned me into a newcomer to my own city, but has also changed the way I will view any landscape.” She gets what it’s about.

Oakland is full of flaneurs like Jenny, and for them all I want to do is add a new dimension to their pleasures. For other Oaklanders, I hope to tempt them into the same habit. Deep down, it’s a form of citizenship.

Winter is a good time to look around while the street trees are bare. The Oakland Hills are beautiful all year round, but early winter brings them a special palette between green and brown. In Deep Oakland I say this about them: “Seen from the city below, especially from the Bay shore, the hills may seem like an even wall, or a wave of rock carpeted with woods. But look again when the air thickens with marine haze and they resolve into a series of en echelon ranges, a set of waves with profiles as crisp as if cut from paper.” This time of year, there have been quite a few days like that.

The geo-flaneur takes walks no one else would think of. I seek out the neighborhood’s eminences and declivities, its peaks and valleys. I also relish unheralded details in the views we all see.

I put in my book the geological things and places I love to visit. That doesn’t discount the joys of the everyday views: handsome buildings, landscaping large and small, the state of the sky and the season, the people along the way. I see and celebrate them too.

This city has everything.

This year marked the fifteenth anniversary of this blog. The actual date of my first post was 25 September 2007, but this year I was too busy at the time rolling through the contents of Deep Oakland to make note of it. And I don’t look back much: I’ve observed the fifth anniversary and my 500th post, and that’s about it. But fifteen years, that’s pretty good. The blog will continue as long as I do.