Archive for the ‘Sausal Creek watershed’ Category

A circumambulation of Shepherd Canyon

18 February 2019

I seem to give myself odd assignments. The latest one was to take a hike around the crest of Shephard Creek’s watershed, better known as Shepherd Canyon. Only during the final mile of that 6-mile walk did I realize what it meant: an outing exclusively on ridge roads.

I got the idea from my circumambulation of Claremont Canyon three years ago. That walk features a variety of rock types and a good set of views into Oakland’s best wineglass canyon — a stream valley with a wide upper watershed and a narrow outlet where it crosses an active fault. Most of Oakland’s major streams that cross the Hayward fault have wineglass valleys that are more or less well-formed (and faceted spurs between them), but you may have to scrutinize them pretty hard to see them, let alone walk their rims.

Shepherd Canyon is another of our wineglass canyons where the roads make this exercise feasible — and an exercise it is, with a thousand-foot elevation gain. The trouble is, you don’t get clear views into the canyon itself. Whereas Claremont Canyon is a viewshed as well as a watershed, Shepherd Canyon’s watershed has an inside-out viewshed. Thanks to our high parklands, this ridgetop walk affords good views around the canyon’s outer side.

Enough preamble — let’s amble. The route starts and ends in Montclair on the geologically friendly 33 bus line. Here’s the layout.

Those little red blips are mile markers. I took this counterclockwise because I prefer steep uphills to steep downhills, and the south end is steep. A bicyclist might prefer the other way, but parts of this route are footpaths.

You could start and end this walk at the end of the 33 line in front of the Safeway, but I started from the Snake Road stop and finished at the LaSalle Avenue stop. Most of the first mile is a bit of a chore along busy Mountain Boulevard, but these days the rain has made the creek noisy, and you’ll hear it down in the woods as you cross the lowest point near the Park Avenue junction.

Be sure and get off the road on this nice path.

It goes around the flattened hilltop housing the Joaquin Miller Elementary School and Montera Middle School.

There once was a rocky hill here, occupied by a Scout camp (which is how Scout Road got its name), but it was vacated and leveled as a handy source of stone and used (I believe) as fill for the Warren Freeway nearby. In any case, the path takes you to the foot of Shepherd Canyon’s perimeter ridge, where you’ll turn right up Mountaingate Way. This view past the foot of Mountaingate looks into the valley of Cobbledick Creek, a tributary of Shephard Creek that runs down along Scout Road. In the next mile you’ll climb 800 feet, pretty steadily.

Soon enough you join Castle Drive and start seeing rocks. Now it’s time for the bedrock map.

The ridge is made up of serpentine rock (sp on the map) plus its typical blocks of blueschist. One of the city’s best blueschist boulders sits where Castle Drive starts, and some of the homes along Castle use the blueschist in their landscaping.

The serpentinite is a sloppier, greener stone that you’ll see along the roadside. Let me warn you that hiking on Castle is a challenge — the road is narrow, there’s no sidewalk, and nobody expects pedestrians. Keep your ears open and step off the road as cars approach.

Where Castle starts to turn north, veer off the road and take the little-traveled West Trail, part of Joaquin Miller Park. You’ll thank me, as I said when I took you down it a few months ago. It’s here that your first views open up.

And the rocks change as you start on the trail. From here on out you’ll be mostly on sandstone. Just for the record, you’ll pass through the Joaquin Miller Formation (Kjm), Oakland Conglomerate (not labeled), Shephard Creek Formation (Ksc), Redwood Canyon Formation (Kr), unnamed Eocene mudstone (Tes), Sobrante Formation mudstone (Tsm) and just into the edge of the Claremont Shale before descending through the same units on the way down.

Castle Road ends at Skyline Boulevard. After a few steps on Skyline, duck into the woods and take the Scout Trail parallel to Skyline, where you’ll meet these guys at the top of the ridge — Oakland Conglomerate.

Where the trail ends at Moon Gate, take Skyline for a few hundred yards, passing the Waterloo Staging Area (unless you’re up for a stroll on the West Ridge Trail, which rejoins this route at Skyline Gate), and take Wilton Drive up onto the ridgetop. It skirts the edge of Redwood Regional Park and has one of Oakland’s best views.

Move on and take Burton Drive, then Shirley Drive. At the end of Shirley is an unmapped trail through Redwood Park that starts with this bench, nestled among boulders of Redwood Canyon Formation sandstone.

Not quite the halfway mark, but just the place to take a rest and a good look around.

The trail descends to the Skyline Gate Staging Area. From there, take Skyline to its confusing junction with Shepherd Canyon/Pinehurst Roads. Don’t take any of those roads — go up Manzanita Drive instead, along the ridgetop. Where the power line crosses the ridge is a fine exposure of the Sobrante Formation’s shale.

This is an unusually good exposure of the Sobrante, which is very sloppy stuff along Skyline, because up here it’s grading into the harder chert of the Claremont Shale.

The two units are stratigraphically continuous, with an arbitrary boundary between them. You’ll see a lot of this rock along the road as you make your way north, then down to the junction of Skyline and Snake Road.

At this spot you overlook Shepherd Canyon on the left, Thornhill Canyon on the right, and the mighty Bay in front as you start down. Do stop at the fire station here and top up your water supply.

The descent along the lip of Shepherd Canyon is straightforward: Take Colton Boulevard to Asilomar Drive to Drake Drive. Again, pedestrians are not expected, but the roads are generally wide enough to accommodate everyone without jostling or stir. Here and there you can see into the canyon. Watch its walls grow close as you come near the narrow part of the wineglass.

When Drake meets Magellan (I know, those two explorers never actually met), the ridge road is finished. It only remains to take the unobtrusive path leading through the trees from 2133 Magellan down to the Railroad Trail — when else will you ever have the chance? — and on into Montclair to catch the bus.

The nice thing about this time of year is that many of the trees are leafless, so you can see more of the surroundings.

That and the weather is cool. I always seem to assign myself weird walks in the high hills during summer, which can be brutal. Better to get out there now.

The Dimond Canyon water gap

15 May 2017

In a city full of geologic features, Dimond Canyon stands out as a classic example of a water gap. But it can be hard to see, even from the prime viewpoint of Leimert Bridge.

Let’s abstract ourselves by studying the overhead views shown in maps. Google Maps, with the terrain view turned on, is where I like to start.

Compare Dimond Canyon, cutting straight through the bedrock ridge of the Piedmont block, with Indian Gulch (Trestle Glen) on the left, a conventional stream-cut valley that fans out against the ridge.

For a starker view of the topography, I like to consult old USGS maps like the 1897 Concord quadrangle, made before most of the area was built up and dug into.

Here we can see that the ridge reaches the same elevation on either side of the canyon — without the canyon cutting through it, this would be a continuous crestline.

There is no sign, either, that Dimond (“Diamond”) Creek cut its way through by headward erosion. That would have left tributaries fingering off on either side, like those visible in the contours above Indian Gulch. Indeed, the single little tributary in the canyon is actually a hanging valley that has to descend steeply as it meets Dimond Creek — not as spectacular as those in Yosemite Valley, but with the same basic configuration.

Finally, we can look at the bedrock evidence in the geologic map.

The whole area around the canyon is mapped as Franciscan sandstone (Kfn), with no hint of faulting or other structure that might have favored the formation of a canyon here. Consider the well-developed valleys above the canyon, guided into existence by the rock-crushing Hayward fault, or the more subtle topographic features where the southern edge of the Franciscan bedrock meets old alluvium.

What we have here, then, is a genuine water gap — a deep pass in a mountain ridge with a stream flowing through it. Geology textbooks will tell you there are two ways to make one. One is for a river to uncover an ancient ridge as it strips the countryside of its sediment cover. The classic case is the Delaware Water Gap in Pennsylvania. The other is for a river to sit there, doing its thing, as the land rises up around it. The Central Valley has good examples at the foot of Del Puerto Canyon . . .

. . . and the Berryessa water gap west of Winters.

What’s odd about the Dimond Canyon water gap is that it’s being carried along the Hayward fault. Every few hundred thousand years, then, it gets itself a new headwater catchment. Today its catchment is Shephard and Palo Seco Creeks. Once upon a time, though, it must have carried the waters of San Leandro Creek. Coming up: Temescal Creek.

Shepherd Canyon landslides

10 April 2017

Last week I went to visit a landslide that had been in the news. As it happened, I saw three.

Shepherd Canyon always gets a lot of landslides, like its neighboring canyons in the high hills. The main reason is that Shephard Creek has a lot of cutting power, thanks to its relatively large watershed and the low base level provided by Dimond Canyon. That creates steep slopes and V-shaped valley profiles. A secondary reason is the relatively soft mudstone underlying those slopes.

My destination was the landslide that came down on the south side of Banning Drive. But along the way my path was blocked by two more mass movements. They’re marked by white asterisks on the geologic map below.

The Montclair Railroad Trail, my usual route, offers walkers good access to the canyon. On the inner side of the sharp curve and cut leading into the canyon, this slope failure exposed the rears of two houses. I classify it as a debris fall.

The majority of the material is broken rock, hence the term debris, and it tumbled in a heap rather than traveling any distance, hence the term fall. Only a little mud was present.

The area is mapped as the Oakland Conglomerate (Ko), although the debris appeared to consist mostly of fine sandstone and a little shale, like this. The rainwashed stone is well displayed.

Picking my way past that was no problem. Farther up the trail, though, was a complete blockage.

Like the lower slope failure, this one involved debris, but unlike it the material slid, so I classify it as a debris slide. Several large trees that came down with the rock didn’t appear to be to blame. However, this time of year is the most dangerous for trees because the ground is sopping wet and the limbs are heavy with young leaves, making them prone to catch the wind. Maybe they triggered the slide. Maybe the other way around.

Fortunately no houses appeared to be threatened above the headscarp, but now the slope is highly vulnerable.

A sewer line runs beneath the trail, so the city may have to clear the slide once the ground is no longer saturated. Meanwhile this is too dangerous to approach. It could fall with no warning.

The debris is made of fine-grained sandstone of the Redwood Canyon Formation (Kr).

Finally I got up to Banning Drive. It’s situated in one of the major side valleys in Shepherd Canyon, and the walls are exceptionally steep.

I classify this slope failure as a debris flow, what the news media often calls a mudslide. It traveled downhill a good hundred meters in a thick semifluid mass. The mud content was greater than the other two slides, and muck spilled into and around several homes on Banning. There’s plenty of footage of the scene online, so I don’t need to show you that. It was hard to watch the residents clearing out their red-tagged homes while the news vans gathered round.

I didn’t need to be there once I’d seen it. Presently I went uphill to Aitken Drive, where the slide originated.

Note a couple of things. Right beyond the gap in the road, a telephone pole was snapped off and the wires were hanging low. (The power was off.) The extra load caused the pole at the left edge of the photo to lean inward. The scar in the road reveals a wall of sandbags (I assume they were filled with concrete) that must have been put there after a previous slide.

Landslides occur where previous slides did. And sure enough, looking uphill I could see the young scar of a small rockslide, nestled in turn within a concavity in the hillside that looked like the scar of a much older slide.

There is another street higher up, Chelton Drive, but no houses up there appeared to be endangered. Meanwhile East Bay MUD had the road blocked while they were making sure the water lines underneath wouldn’t break and make more trouble.

Who’s responsible? Perhaps no one. The problem is above my pay grade, as I’m not a licensed geologist. But I can see the signs and warnings of landslides, and so can you if you pay attention to the landscape. The U.S. Geological Survey has resources, and so does the California Geological Survey.

Oakland geology ramble 1: Leimert to Redwood

6 June 2016

For a while now I’ve been envisioning geological rambles around Oakland — walks (hikes, really) that aren’t loops, but traverses. They rely on public transit, because that’s mainly how I roll. You can walk them in either direction. My ultimate idea is to work out a network of rambles that will cover the whole town. You could combine them into epic outings. This is the first ramble. It’s a little more than 4 miles.

The west end of the route is on Park Boulevard at the Leimert Bridge. The 33 bus line will get you there from either the MacArthur or the downtown BART station. Starting elevation is ~375 feet. Here’s the street route (1000 pixels):

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And here’s the corresponding geologic map:

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Briefly, the route takes you past Franciscan sandstone of the Piedmont block (Kfn), then crosses the Hayward fault into much older mixed rocks of the Coast Range ophiolite (basalt (Jb), serpentinite (sp), Leona volcanics (Jsv)) and a bit of Late Jurassic mudstone of the Knoxville Formation (KJk). (Search this site for more about all those rocks.) Remember to leave the stone alone.

Oakmore Hill looks pretty intimidating as you cross the Leimert Bridge. Part of that is because of Dimond Canyon below. The bridge is about 125 feet above Sausal Creek.

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Buy your fuel and water in the charming little Oakmore commercial district. Then make your way to Braemar Street along the top of the hill. Take any route you like. The intersection of Arcadia and Melvin, directly above the E in “Oakmore,” is a good shady spot to regroup and refresh.

Along the way you’ll see exposures of the sandstone.

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Braemar Street is nice and level. Truck along right to the end and enter the footpath like you do it all the time. As you descend the steps, look across the fault-line valley to the bare slopes of Joaquin Miller Park. That’s where you’re headed.

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Closer to hand, you’ll see that the rock has changed. This appears to be the Jurassic basalt, unit Jb.

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On the way to the freeway overcrossing at Lincoln Avenue, look at the lay of the land.

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The active trace of the Hayward fault isn’t precisely mapped here, but it runs from about the lower middle edge on the left side to the horizon directly behind the large tree (note the LDS Temple spire on the right edge). The next time the ground breaks, you’ll see it very clearly here.

Cross the freeway and take Woodminster Lane to Woodside Glen Court, where the road ends at a backdoor entrance to Joaquin Miller Park at about 700 feet elevation. Things get pretty steep here, and they’ll stay steep.

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The exposure appears to be either Leona volcanics or Franciscan sandstone; the important thing is that the bedrock changes abruptly as you enter the woods into the area mapped as serpentinite.

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Specifically, this is blueschist, the electrifying high-grade metamorphic rock that’s intimately mixed with greenish serpentine rock throughout this map unit. Enjoy the trail, which is the little-traveled west end of the Sinawik Trail, as you puff your way up to about 950 feet at Lookout Point. Stop a bit and check out the high-grade boulders there. (You’ll want to stop anyway.)

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This is where I show the route forking. It’s easier to go right, either on the trail or on Sanborn Road, going downhill to Joaquin Miller Road and across it to Butters Drive. I took the high route, up what I call Visionary Ridge, because I was returning two pieces of basalt to the locality where I got them. I thought better of that plan as I passed the park’s native plant nursery, where I added them to the little border at the bottom of this photo.

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The hillsides here are pure serpentinite and worth a close look. The high route continues along the ridge crest, around 1100 feet, to Joaquin Miller Road, where you cross and take Robinson Drive to where it meets Butters Drive at about 1025 feet. The high route will save you a loss and gain of 200 feet, but you’ll miss Butters Drive.

Butters Drive starts in some of Oakland’s most spectacular serpentine/blueschist ground, and it’s landscaped too. (See more photos from a 2015 visit here.)

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Continue past the hairpin turn into the headwaters of Peralta Creek in the Butters Canyon private preserve. Here the rock along the road is mapped as Leona volcanics.

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The intriguing thing is that right across the creek the rock is Knoxville Formation, a unit that’s generally shale and hence easily eroded. I think this contact is exploited by the creek to dig the canyon so locally deep. You can get a good look at the Knoxville right above the intersection with Robinson Drive, where the high and low routes meet again.

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Now the route plunges about 300 feet down Crestmont Drive and through Oakland’s largest area of serpentinite. Take in the prodigious exposure at Crestmont and Kimberlin Heights drives.

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The west edge of the serpentinite zone is a thrust fault, which means the rock here is quite pulverized. This part of the hike has several interesting exposures that I’ll let you discover on your own. The very easternmost end of Crestmont Drive goes through Leona volcanics, which you’ll see in boulders.

When you reach Redwood Road, truck on downhill to Campus Drive at about 650 feet elevation, where the 54 bus comes by regularly. It’ll take you to the Fruitvale BART station or connect you to major lines on MacArthur, Foothill or International boulevards.