Archive for the ‘Other topics’ Category

Tracing the old Thorn Road

6 August 2018

Hiram Thorn took it upon himself in 1853 to build a road over the Coast Range hills from today’s Montclair to his redwood mill, which was either at the present site of Canyon or farther downstream where the former town of Pinehurst once sat. Thorn’s Road was a toll road for a long time, connecting Oakland to the Moraga Valley agricultural hinterland and beyond. “This was the main road into Contra Costa county in the early days,” wrote the Tribune in 1923, “and a daily stage ran over it to Walnut Creek, Danville and the top of Mount Diablo.”

This piece of the 1897 USGS topographic map shows the Thorn Road running from the lower left to the lower right corner.

There are a few things to point out. Kohler Creek is called Temescal Creek today, but back then Temescal Creek went straight uphill from the Lake Temescal reservoir. That streambed was obliterated by the later construction of upper Broadway, Route 24 and the Caldecott Tunnel bores. The dashed line from top to bottom is the county boundary, and the thick dot-dot-dash line running up the canyon along with the road is the boundary between Vicente and Antonio Peralta’s shares of the San Antonio rancho, the immense royal land grant made to their father in 1820. The Thorn Road was also the official line between the Oakland and Brooklyn Townships of Alameda County.

This 1878 map made by Malcolm King shows the landmarks at the time, including the location of the toll gate about where the Thornhill Coffee House stands today.

In the 1880s it was already being referred to as “the old Thorn road.” In 1889 the Tribune reported on the Alameda County Board of Supervisors meeting of 1 April: “The Committee of the Whole, to whom had been referred the petition asking for the placing in good repair of the Thorn road to Moraga valley presented a report saying, that upon examination of the ground, they were satisfied that it would be utterly impossible to ever make the same a good road on account of the steep grade.” They recommended surveying “a road to the summit over a new route and on an easy grade.” That new road was the Snake–Skyline–Pinehurst Road route. Between it, the existing Redwood Road, the Kennedy tunnel to the north and the Oakland Antioch & Eastern railway to the south, which went up Shepherd Canyon and cut through the hills to Eastport, the Thorn Road was no longer the best way over the hills.

Nevertheless, the 1936 street map showed Thorn Road still following its old route up to the Huckleberry saddle.

The 1947 topo map shows that the top segment of the Thorn Road, and all of it on the far side, had been abandoned. The newly named Thornhill Drive took a zigzag route incorporating what had been Idlewild Drive, and the part of the Thorn Road left behind was named Sobrante Road.

Here’s the modern Google map just to give an idea of the streets and terrain.

The Thorn Road took the gentlest way up Thornhill Canyon to the topographic saddle where the entrance to Huckleberry Preserve is today. It was still a very challenging grade near the top, about a 36% grade or 20 degrees, according to my phone compass. (This would rank among the steepest streets in notorious San Francisco.) It was even steeper on the Contra Costa County side.

For a while after the 1947 topo map was published, street maps connected Sobrante all the way to Skyline, but as of 1967 the upper end of Sobrante had been cut off. However, there’s still a right-of-way and a sewer line running down it.

That’s where I took a walk last week. This is looking back at the end of Sobrante and across Thornhill Canyon.

There are remnants of the old grade, but no path bigger than a game trail. I think a footpath should be built here, as an emergency route if nothing else.

Underfoot is Claremont chert, not a surprise because this is right next to, and a hundred feet downhill from, the endangered chert roadcuts of Elverton Drive.

The habitat has possibilities. The ground was wet during my visit, thanks to fog drip. But crews have dumped a bunch of eucalyptus slash, which not only obstructs passage but also presents a fire hazard.

Also prominent in the human litter is a bunch of slash consisting of For Sale signs. There are still lots available up here.

On the far side of the ridge, in Contra Costa County, a stub of the Thorn Road got the name Winding Way. It was known as a shortcut for motorcylists when CHP Captain George Kallemeyn, chasing a group of hotrodders down the road, went over the edge and died in July 1959. Winding Way was still shown as open as of 1967, though it went only a short distance down the canyon.

Some time after that a landslide took out the highest segment of the road, and today the Huckleberry Path edges around the scar. About a hundred yards down the trail, a bench marks the spot where the old roadbed, heavily eroded and overrun in roadcut rubble, picks up again. It’s passable on foot all the way down to the hairpin turn of Pinehurst Road.

I recommend visiting this end of the old road starting down at Pinehurst. You can park beside Pinehurst a little bit downhill from the hairpin, where the old rail tunnel came out. (The cut is still there, filled with rubble and leaking a steady stream of groundwater.) But just as convenient, and more tempting, is the new Wilcox Station staging area, an access point to Sibley Volcanic Preserve’s eastern annex where the Eastport station once stood.

The road starts out along San Leandro Creek, then soon starts to climb.

It’s a steady grade, but the road was never more than one lane wide. As you walk it, imagine the work it took to trailblaze by pickaxe and oxteam. Imagine driving the daily stage to Danville over it. Between raveling ground on the uphill side and landslides on the downhill side, this road, once a vital link in the commerce of the redwood era, is reduced to a precarious trail today.

At any time an earthquake or rainy winter could cut it off, either until repairs can be made or once and for all.

The human presence, benign to sanctified

28 May 2018

In my last post I described the spectrum of waste to be seen around the landscape. Piles of garbage are easy to see and judge as litter. Bones and downed trees are natural, but for citydwellers it takes an effort not to wish them removed.

Then there are all the things on the spectrum of art, like these amaryllis bulbs donated to undeveloped Knowland Park. Yeah, they’re an alien species, but neither is their presence a heedless desecration. People decorate things; it’s what we do. We make spaces where there were none before.

We make local habitations, some even with names, in wild Oakland.

I’ve come to enjoy the signs of artistic impulse out in the field. Many are harmless roadside attractions, too small to catch attention except at walking speed.

Others turn the nondescript into something . . . descript. I wish I knew more about this little assemblage that was up in Knowland Park a few years ago.


I think a solo artist made that.

I think a small group adopted this tumbledown shed on Grizzly Peak; their affection shows.

And then there’s the communal gallery up in Leona Heights Park; been going on for years; different every visit. Anyone can participate, but you can tell the standards are intimidatingly high. The first time I found it I went yeesh; now I take my cue from the Grateful Dead: “nothing left to do but smile, smile, smile.”

The best place for this kind of art is the Albany Bulb. I haven’t been in a few years. Wikipedia suggests that the art has been fading and is no longer what it was. With that in mind, here are some photos from about ten years ago.

The general scene is a former dump site for construction waste. Today, most material of this sort is recycled — old concrete can be used as aggregate in new concrete and rebar is easily melted into new steel. At the Bulb, this material was recycled into art.

Lots of the work was crude, but effective.

The setting, on the Bay shore, was a crucial part of the work.

This is one of my favorites, now long gone.

The landmark of Mad Mark’s Castle was once a sublime place.

litterart-13.jpg

Today I’m told it’s not really there any more. Sic transit gloria mundi.

The litter spectrum, benign to unholy

14 May 2018

The litter on the land falls along a spectrum. This disembodied deer hoof does not qualify as litter because, as far as I know, a human didn’t leave it on this abandoned, overgrown fire road. I felt no obligation to do anything more than pause and contemplate it.

At the opposite end of the spectrum is this spectacle just off Pinehurst Road on well-posted watershed land. I felt ashamed on behalf of humanity, but could do no more than pause and contemplate it.

Fortunately, that same day East Bay MUD had a crew nearby with a backhoe and related equipment, cleaning up an even worse litter pile.

That leaves a wide space between the two ends of the spectrum with different judgments to make and responses to consider. This next photo of cannabis seedlings is a few years old, and maybe these days people are doing a little less surreptitious planting in our out-of-the-way places.

It’s possible to do this without making an unholy mess, but I’ve come upon several instances in Oakland’s hills and they were all unholy messes of degraded plastic, bags of spilled fertilizer and remnants of crude camping practices. And the plants didn’t look very good either. So these seedlings . . . I left alone with a sense of foreboding similar to what I’d feel upon seeing fresh bear scat.

Stuff like this dead mylar balloon, lost from some celebration and fallen to ground way off the trail in upper Grass Valley, makes me feel ashamed . . .

but I’ve learned to stop stewing and just pick it up. One by-product of my quest to reduce my collection of rocks (I no longer call it a rock collection) is a growing set of used baggies. I pack several and fill at least one each outing.

Turns out that while I’m not that much of a hiker — just a flâneur of the hills — I’m right up there with the hardcore wilderness walkers who carry trash bags as their eleventh essential. It’s a practice I urgently recommend you follow too. Maybe we can’t fix the unholy messes that way, but it beats shame.

And here and there, you come upon trash that is picturesque.

And occasionally you come upon a thoughtful act of self-expression, around some corner where it’s been waiting to meet you. That’s what my next post will be about.

In other news, I’ll be leading a walk for Oakland Urban Paths next month visiting some of our historic former rock quarries. That’s in addition to the Oakland Heritage Alliance walk I’m leading in July. Also in the works, a walk for the Friends of Sausal Creek.

How useful is the Orinda Formation?

30 April 2018

Walking along the paved trail north of Inspiration Point, I was brought up short by a splendid outcrop of conglomerate.

It’s strongly reminiscent of the Orinda Formation conglomerate exposed to the south in Claremont Canyon, in Sibley Volcanic Preserve and along Route 24 east of the Caldecott Tunnel.

Naturally I fired up the geologic map (I keep USGS map MF-2342 on my tablet) to see how the locality is mapped. It’s the little hill northwest of Inspiration Point, right above the word “Nimitz” where a power line runs.

But instead of Orinda Formation (the orange unit labeled “Tor”), which underlies Inspiration Point, it’s mapped as “Tus,” or “unnamed sedimentary and volcanic rocks (late Miocene).” Turns out there’s a major fault that separates two big blocks of young East Bay rocks — that thick black line with the teeth that represent the upthrown side — and even though the rocks look the same, we can’t say for sure they are.

The area of “Tus” rocks is rather large; in fact it’s the largest single rock unit on the geologic map.

I poked around the literature and found that the Orinda Formation has drastically shrunk over the years. As one example, here’s part of a 1973 map of the Lafayette area (Calif. Div. Mines & Geology Map Sheet 16) that classified a bunch of rock as Orinda Formation, drawn with the exquisite attention that emanates authority.

But the details are quicksand. First, the map is not about bedrock per se, but landslide hazards. Second, the author’s citations are generally very old, not that there’s anything wrong with that, but still. Third, the author’s idea of the Orinda is a unit that mixes lava beds (lumped today in the Moraga Formation) with the coarse sediment that defines the Orinda today. A long footnote explaining his thinking shows that he basically made an arbitrary choice of stratigraphic nomenclature to match the informal usage of local engineering geologists, who tend to talk about “Orinda-type” materials (like I was thinking at my outcrop) without making sure the stuff actually matches all the criteria for the Orinda Formation.

I’ve read my share of geologic engineering reports; any large construction project has to have one prepared. They’re good for their purpose — ensuring that the work is suited for the ground — but they don’t critically assess all the details of the science. And they probably shouldn’t. Instead, they line up the existing literature, outmoded and current alike, and discuss or dismiss it on the way to reaching their conclusions and advising their client.

Maps like Sheet 16 propagate obsolete or informal nomenclature, and thus stratigraphic concepts that are outmoded or discredited persist in the geotechnical literature like zombies long after research scientists have moved on. But I don’t blame people. The old idea of the Orinda Formation, widespread and simple, was very handy. The current idea of the Orinda, constricted and specific, is less handy because it leaves a large area of bedrock with the mumbly label “unnamed sedimentary and volcanic rocks (late Miocene).”

Geologic maps aren’t written in stone. Only stone is, and we’re still learning to read it.