Archive for the ‘the Fan’ Category

The Jungle Hill landslide

23 November 2020

Jungle Hill is an odd plot of city-owned land off 38th Avenue in East Oakland. It’s been something of an embarrassment since it collapsed in landslides in the 1910s, marring the carefully tended image of a new and very desirable neighborhood. Landslides are more common in Oakland’s low hills than people think.

Jungle Hill is east of Fruitvale and west of High Street, making it sort of an in-between spot in terms of today’s neighborhoods. Here it is, marked with a red asterisk on the street map.

The area was empty countryside until 1906, when things changed dramatically with the San Francisco earthquake on 18 April. Oakland’s population essentially doubled overnight, and the big landowners leapt into action, putting their long-planned schemes into action as fast as they could. The default scheme at the time was to set up a streetcar line serving a tract of land, then subdivide the tract and sell the lots to people who would build homes on them. The developer would impose various restrictions to assure buyers that they would have neighbors like themselves building houses like their own.

Such was the case in the area of Jungle Hill. Beyond the presence of the streetcar line, the big attraction of the area was its elevation. Here’s the exact same area on the geologic map.

Long-time readers will recognize the orange blobs as the set of ancient gravel hills that I call the Fan. They stand above the flats by a hundred feet or more, which made them desirable home sites, and they’re still Oakland’s homiest middle-class neighborhoods, delightful for rambling. Foothill Boulevard runs along their lower edge. Jungle Hill sits on the western edge of Lobe 6 of the Fan. With that background, let’s zoom in and get oriented.

The streetcar line, spine of the development, went up 38th Avenue, which was named Liese Avenue at the time (a little spur up by the freeway still has that name). The street is still extra wide and displays the slope above Foothill Boulevard well. In 1906, Foothill Boulevard was the brand-new road to Hayward, a great source of city pride and the key to developing the lower hills.

The tract extended several blocks on either side of Liese Avenue. This area was developed starting in 1906 as Boulevard Park, “the most desirable property for home sites that has ever been placed upon the market.” Soon the ads proclaimed, “Elevated land! Magnificant marine and landscape view. All streets macadamized, curb and stone gutters, with 5-foot sidewalks. Water, gas and sewered. Trees and palms in profusion. New electric car line through the tract.”

After listing the prices and terms, they ended, “No Mongolians need apply.” This is how Oakland used to be.

Now we zoom in to the Jungle Hill site.

During heavy rains in January 1911 the hillside north of Ransom Street, overlooking that dogleg at the north end of Santa Rita Street, gave way. Three years later, early in the morning of 20 January 1914, in the midst of a series of storms that ravaged the whole west coast, the hillside farther downhill started moving. The Joneses across the street nearly died when their gas line broke. More sliding happened a few days later.

Here’s what the hillside looks like today from the north (well, in 2014 when I last wrote about this area). Santa Rita Street is hidden at the foot of the hill. The slope to the right of this view (visible in the newspaper photo) is even higher and steeper, but no one seems worried about it and I saw no obvious signs of ground movement in a visit this week.

This setting is very reminiscent of the McKillop Road landslide, which is also on the edge of a lobe of the Fan. Indeed, both sites hosted landslides soon after their development, in the years before 1910. Unlike the McKillop slide, which was notorious in the 1930s and again in the 2000s when it reawakened, Jungle Hill never appeared in the newspapers again, although a MacArthur Metro story from 2007 claims that more sliding occurred in the 1930s.

In any case, the property was long vacant when an early land trust, the Santa Rita Land Trust, scraped together the money to buy it in 1977. Residents put a lot of work into it, installing a path of railroad-tie steps that’s now crumbling. But when the trust petered out and went defunct, the land went to the city.

The hillside has the hummocky appearance typical of landslide sites.

An old wall that once bolstered a homesite looks to be in good shape.

And the climate and views that once made this area so desirable are still there.

The streets above and below aren’t blatantly crumbling. The site appears to have been so stable since 1914 that it could be built upon today. That would be politically difficult, I’m sure.

While I was visiting, I had to see the Carrington Stairs again, known to generations of local kids as “the 72 steps.” It’s still impressive from the top, if a bit grim.

But when you get down, it is fantastic. Click this picture for its full 1200-pixel glory and pay it a visit whenever you’re around.

Pill Hill

27 April 2020

Pill Hill, an odd outlier of ancient alluvial gravel in North Oakland with a long history, rises almost 50 feet above its flat surroundings. Today it’s thoroughly encrusted with buildings, as seen here looking up Broadway from the YMCA gym building and down Broadway from the Kaiser hospital parking structure.

Beginning in the 1860s it was known as Academy Hill or College Hill for its private schools in gracious settings, which included St. Mary’s College, the Pacific Theological Seminary (now the Pacific School of Religion on Berkeley’s Holy Hill), the California Military Academy, the Pacific Female College, Hopkins Academy (where publisher J.R. Knowland started his first newspaper as a student), and other long-gone institutions.

Although the hill started out as bare grassland, after a few decades of landscaping the location was described in 1885 as “healthful, retired, and beautiful” and was served by horsecar lines on both Telegraph Avenue and Broadway.

Anthony Chabot built the first reservoir of his Contra Costa Water Company here in 1868, near today’s Summit Street and Hawthorne Avenue at the hill’s highest point. It held a million gallons of Temescal Creek water, and Academy Hill institutions may have been early customers supplementing their own wells. See its location on the 1878 Dingee Map:

and here’s the spot today.

The 1949 USGS topographic map shows the hill lovingly outlined in 5-foot contours. Given all the construction and digging done here since then, I think not even a modern lidar survey will ever match the fidelity of this map.

You can see that all the academies were gone by then (except for Grant Senior High, now the Zapata Street Academy), replaced by hospitals. Hence today’s name of Pill Hill. Probably the availability of large land parcels, the subsequent improvement of the water supply, the great street access, the advantages of a concentrated healthcare district (including the original Samuel Merritt College) and the attractive setting favored this change. When Pill Hill’s three big hospitals combined in 1992 to form Summit Medical Center, it was the hill they shared that inspired the name. The views from the hill, especially from the higher hospital floors, remain excellent.

Pill Hill is part of the widespread body of old Pleistocene-age gravel that I call the Fan, specifically lobe 2. Here it is on the geologic map.

Where this material extends across 27th Street, there’s a low hump in the road that the builders didn’t bother to flatten.

And at its north end, the construction of I-580 wiped out the hill, but a little bit still extends into Mosswood Park. This cut in the low rise at the park’s south edge may expose the gravel, but of course I can’t dig into it.

The rest of the hill’s periphery is an abrupt edge; this view west from Broadway down 30th Street is typical. I showed a few more views of the hill in this post from 2011.

The gravel of the Fan is considerably older and more consolidated than the alluvial plains around it. Exposures are very difficult to find, which is maybe why I’m a bit obsessed. The official description of this map unit (Qpaf, Quaternary (Pleistocene) alluvial fan) includes the tantalizing bit that they “locally contain fresh water mollusks and extinct late Pleistocene vertebrate fossils.” I did present one good (short-lived) exposure here in 2015.

Anomalies of Sausal Creek: Dimond Canyon

14 October 2019

This is the second of four posts about the peculiarities of Sausal Creek, going from its headwaters to the Bay. Here I’ll address Dimond Canyon, the 2-kilometer segment between the Warren Freeway and the flats of Dimond Park. The steep walls of the canyon, which is several hundred feet deep, are entirely hard sandstone of the Franciscan Complex, part of the Piedmont block.

This is the same stone quarried for decades in Rockridge (the Bilger quarry) and the land that would later become Piedmont (the Blair quarries and the Davie Stadium quarry). In fact the Diamond Cañon Quarry was one of two here in the canyon. It’s now occupied by the Zion Lutheran Church, as seen here from across the canyon.

The quarry scar appears on this terrain map as a big round nick in the canyon wall next to Park Boulevard.

A while ago in this space I described Dimond Canyon as a classic water gap — a stream-cut gorge crossing a bedrock ridge that otherwise seems impenetrable.

Geology textbooks will tell you there are two ways for streams to make a water gap. In the first way, the stream was there first (an antecedent stream) and a ridge of resistant rocks rose up around it. In dynamic California, this is a straightforward explanation of our water gaps. In the second, the ridge was there first, inherent in ancient deformed rocks buried under younger strata, and the stream (a superposed stream) cut down to, then into it while stripping off the overlying material. That’s how they explain the Delaware Water Gap and other examples in the gentle Appalachians.

Dimond Canyon is actually a semi-classic water gap. Yes, the ridge it crosses must have risen while the stream was cutting down, but the story is complicated by the fact that the watershed upstream lies across the Hayward fault, and is constantly being moved to the right. This means the canyon has hosted streams from several different watersheds over the past million years or so.

Therefore the streams feeding Sausal Creek today could not have dug the canyon; some predecessor watershed did it. There must have been gaps and surges in the water (and sediments) flowing through this canyon. If we ran things backward a million years, what would it show? The exercise would be blurred by serious uncertainties, but the matter is not beyond all conjecture.

I beg your indulgence as I present some slides from my talk to the Friends of Sausal Creek last month. They’re Google Earth views looking west across the fault. Here’s today, with the fault trace shown in red.

The view may be a bit confusing as I rewind the motion on the fault at about 10 millimeters per year. The far side looks the same because we’re focusing on it while it moves leftward, toward San Leandro. For a long time, Sausal Creek has been carried past small watersheds that, like today’s, could not possibly have carved Dimond Canyon. But about a million years ago, Dimond Canyon would have lined up with the watershed of Arroyo Viejo.

This looks promising because the watershed (the part above the fault) is about twice the size of Sausal Creek’s, giving it roughly twice as much water and cutting power to match.

But to make the canyon, you have to have something pushing up the ridge while the stream across it keeps cutting its way down. There’s nothing obvious that would have been pushing up the bedrock ridge at this time.

Going back a bit further, though, we line up with the great big watershed of San Leandro Creek, a dozen times larger. This stream has plenty of cutting power, evident in the canyon it’s dug where the dam and reservoir sit.

And finally, we have a mechanism here for uplifting the ridge that Dimond Canyon cuts across. The hills of San Leandro consist of a large slab of gabbro so big and strong that it deflects the Hayward fault slightly. Back when the sandstone of Dimond Canyon was grinding past the gabbro of San Leandro, the jostling between these two bodies of rock, caught in a vice by the geometry of the fault (a restraining bend), would have pushed both sides upward because that’s the only way out of the vice. And all the while San Leandro Creek would have been cutting a nice deep water gap as that hard rock rose.

Eventually, inevitably, the fault carried the water gap out of reach, and ever since then Dimond Canyon has housed lesser creeks for episodes of a few hundred thousand years. Sausal Creek trickles down the canyon today not doing much to it, the shrunken tenant of a structure built by a mightier maker.

This story (and that’s all it is really) appeals to me because it would also explain the presence of the Fan — the swath of gold on the geologic map representing Pleistocene sediment.

I’ve always regarded it as a fossil alluvial fan because of its shape on the map, but maybe that’s accidental. Maybe it’s just a chunk of old East Bay land that was lifted along with the Piedmont block, or washed off of it afterward.

I first posted about the problem of Dimond Canyon more than 10 years ago. Takes a while to figure out some things.

Land and rocks of westernmost Piedmont

2 April 2018

The western end of Piedmont includes the headwaters of Pleasant Valley Creek, which is tucked under Grand Avenue. But the slopes and gullies of the valley can’t be hidden, and what may seem like a scramble of streets is a nice place to walk around. The topography I’m talking about is north of Oakland Avenue, between Grand and the former quarry of Dracena Park.

None of it’s bedrock; nothing wrong with that. It’s the uppermost part of lobe 3 of the Fan, that big arc of ancient alluvium hills across central Oakland. The bedrock part, farther uphill, is much steeper walking, and the rock (the blue field labeled “Kfn” on the geologic map) doesn’t show itself either.

I should make an exception to that statement — Dracena Park is a great place to see the bedrock. But for the purposes of this post it’s just a pretty place, either in the former main pit:

or in the valley on the north side, now full of redwoods.

This is the most dramatic bit of stream valley in the area. Elsewhere, it’s easy to trace the drainage lines; in fact during our recent batch of rain, you could see water coming out of the ground just like in the old days before people lived up here.

This slopy bit of suburbia is criss-crossed with hidden history. The Key System streetcars used to serve the neighborhood. Indeed, a railroad syndicate once planned a major route through here that was going to run through upper Fruitvale and on to San Jose. The right-of-way appears in this 1927 map (courtesy of the Oakland Library History Room), long after the plans were abandoned.

The part of it running as far as Oakland Avenue did end up with rails as part of the Key System’s C line. If you look closely at the area in Google Maps, the lot lines give the route away.

The transit routes, road and rail, took advantage of the saddle in the ridge of lobe 3, at this spot where Pleasant Valley Road eases over the hill and becomes Grand Avenue. The view is west across the saddle toward Rose Street.

OK, enough of that. There are indeed rocks in this neighborhood. See that clever stone wall in the foreground in the previous shot? Here’s a closeup.

Other rocks are more laid back, understated but cool.

Still others, the only word for them is homey.

They’re all mostly landscapers’ stone, purchased at a commercial yard. But here and there you’ll see genuine domestic Oakland rocks. This little wall is made of serpentine/blueschist from around here, probably the pit at Serpentine Prairie or nearby.

And the Franciscan red chert is very likely from Piedmont itself, which sits on a hill of melange, a marble-cake rock unit that mixes chert, basalt, sandstone and serpentine in a mudstone matrix.

Some of it can be downright psychedelic. Stuff like this was quarried in Piedmont before any buildings were here at all.

Even the sidewalks, the oldest ones anyway, incorporated aggregate from Piedmont’s original quarries.

The town has grown up since then. It puts on a good front — very nice homes, lovely grounds, a fine place for walking and taking in the views (especially when the leaves are down in winter). But it began as a rugged, dusty mining district with horses and dynamite.