Archive for the ‘Oakland geology views’ Category

Skyline panorama from Lake Merritt

4 July 2022

Here’s a project I’ve wanted to do for some time: an annotated panorama of the Oakland skyline. Of course, we have many skylines, as seen from different places, but the first one has to be the view from the mouth of Lake Merritt.

It’s a 4000 X 1200 image weighing 2 MB; for convenience in printing, should that be desirable, I’ve also split it into left and right halves.

The top row of labels is for things on the skyline, and the bottom row, in the water, is for things along the shore. The labels in between are positioned according to their distance. As it happens, I can refer you to previous posts about most of these features.

Top row:

Grizzly Peak
Vollmer Peak
Barberry Peak
Skyline Boulevard roadcut
Round Top
Old Thorn Road Pass
Manzanita Ridge
Pinehurst Pass
Redwood Peak
Redwood Pass
Sugarloaf Hill
Caballo Hills

Middle space:

Claremont Canyon
Route 24 roadcuts
Temescal Canyon
Mountain View Cemetery
Piedmont block
Shepherd Canyon
Pershing Drive
Dimond Canyon
Lookout Point
LDS Temple

The three lower hills belong to the Fan, the crescent of Pleistocene gravel that is Oakland’s most distinctive geologic feature:

Adams Point Hill
Haddon Hill
Bella Vista Hill

Finally, right on the lake itself are these notable features:

Lakeside Park marine terrace
Our Lady of Lourdes
Pine Knoll Park marine terrace

I can see there are a few more things I should write about.

A closer look at Haddon Hill

6 June 2022

My book manuscript (now in the copyeditor’s hands) has a chapter about the Fan, our peculiar region of gravel hills that stretches from Pill Hill to Evergreen Cemetery. In the book I refer to it as Oakland’s second level. I briefly recount its human history, starting with the trouble it caused the initial Spanish exploring expeditions (led by Fages in 1770 and 1772 and by Anza in 1776), then go on:

“Today, whether we drive, ride or walk across the second level, we can still see the underlying landscape and picture how it looked to our predecessors. The eastern, uphill side of the Fan, toward the Hayward Fault, is a string of hills of the third level, most of which are bedrock. The downhill side, toward the Bay, is a variegated landscape of low rises and small gaps through which the Bay sparkles and distant mountains across the water loom, in detail or in silhouette as the weather changes.”

What drives this passage is the bit about picturing how things looked to our predecessors. That might sound romantic — and it surely is — but it’s also a basic skill of geologists, especially in the urban setting.

I sometimes think that as I look around at the Fan, I’m craving glimpses of the hills as they appeared to the Ohlones during the thousands of years they were managed as meadows, the way they appeared in the 1850s when the Town was founded. The Ohlones kept the hills clean to support their lifestyle. Today we keep the hills populated and planted in trees to support our lifestyle. Before humans lived in this country at all, during the ice ages and the warm breaks between them, these hills were either oak-bay woods or cold savannah depending on the climate. The best time for geologists was during the Ohlone years, when the Fan was laid bare.

There are no images from that time. We can only imagine how it looked and felt. To illustrate the tools I use, let’s take Haddon Hill, in the heart of the Fan next to Lake Merritt, as an example (specifically, it’s the Haddon segment of Lobe 4).

First there’s the Bache map from 1857. Although it was primarily a navigation map, it showed details of the surrounding land as well, including Haddon Hill.

The physiography isn’t very precise, but the shoreline and roads can be considered reliable.

Second is the digital elevation map (available in the National Map viewer), which strips the buildings and vegetation off the land.

The composite map, made using the transparency slider, is less stark and easier to deal with.

Haddon Hill is a triangular area defined by the lake, the freeway and Park Boulevard. It has two easy avenues through it that go up little valleys, the northern one on Wesley Avenue and the southern one on Athol Avenue. All the other roads tend to be straight and ruthless. If you walk or bicycle here a lot, you know this already.

When Oakland was a tiny town huddled at the foot of Broadway, Haddon Hill had a road running south through it, undoubtedly based on an Ohlone path, that climbed up from Indian Gulch where Wesley tops out, worked along the 100-foot contour and eased over the hill where Haddon Road meets Brooklyn Avenue, then went down into the southern valley where Athol runs today. (The path branching off to the east along the hill’s crest is probably the route Anza took in 1776.) That all changed when the settlers moved in and cars took over everything. Today gravity doesn’t matter as much, and when we read Friar Juan Crespi’s account of traversing the hills here, “which, although they are all treeless and grass-covered, annoyed us very much with their ascents and descents,” maybe we don’t feel it like he did in 1772.

The old road came down Athol from the right in this view north from the intersection of Athol and Newton Avenues.

Finally we get to the geology part.

Qpaf, Pleistocene alluvium (the Fan); Qmt, Pleistocene marine terrace; af, artificial fill

The “Qmt” part is the same marine terrace that runs through Clinton, and I have to say I disagree with the map. I think the terrace extends only to the “P” in “playground.”

Whenever I venture into the Fan, I’m beguiled by the neighborhoods but always look past the homes and landscaping for the wider views. Here are a few examples from 21st-century Haddon Hill. They tend to come in glimpses. This glimpse from across Park Boulevard, at 9th Avenue and E. 28th Street, shows the St. Vartan church, conveniently on Haddon Hill’s highest point, and Grizzly Peak.

This view down Booker Street shows the lower part of Haddon Hill hiding Lake Merritt in front of downtown. Brooklyn Avenue is just visible in front of the Ordway Building.

This view downtown looks down Cleveland Avenue across the Wesley Avenue valley.

And finally, here’s looking across the Athol Avenue valley at St. Vartan from the top of McKinley Avenue.

Wherever you go, smell the roses.

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.

The Oakland Hills

13 April 2020

These days we’re all sheltering in place: doctor’s orders. What better thing to do than rummage through those thousands of camera images on our hard drives? This phase of our lives is going to last a while, and I have little sense of what I’ll be writing here instead of reports from the field, my tried-and-true resort. I’ll start anyway, with a dozen shots of Oakland’s incomparable defining feature: its backdrop of hills. From near, from far, from every part of town, the Oakland Hills make up our civic stage set.

What they do: The early boosters in the 1800s wrote florid panegyrics about both the beauty of the hills and their salubrious effect on our local climate. They elevate the Pacific winds so that San Francisco’s notorious ground-hugging summer fog never bothers us, and they gather orographic rainfall that keeps the streams flowing. The hills give our topography a concave shape, like a skateboard ramp, that makes every place in the city visible from every other place.

How they look: The hills shift their colors and shadows throughout the day and around the year. Right now they stand out in crisp focus because the air, almost free of traffic pollution and seasonal haze, is so clear. Look at them on a hazy or misty day and they resolve into a set of ridges, arranged in depth. They turn the most prosaic places pretty, and they set off our best buildings to advantage. They peek from behind every photo, a welcome intruder. Without them, this would not be Oakland.

What they are: The Oakland Hills are tectonic hills. They arise along the far side of the Hayward fault because there is a modest amount of compression across the fault in addition to its dominant sideways displacement. They’re not the product of thrust faulting, bulldozed up like the San Gabriels or the Rockies or the Himalaya; not the product of crustal stretching like the basins and ranges of Nevada; not erosional eminences like the Appalachians. They’ve been sort of smeared up. They have a wide variety of rocks in them, arranged in a pre-existing order that isn’t closely related to their shape.

These images are presented from north to south. As usual, click them for the 800-pixel version.

I offer these images not to encourage you to visit the hills (unless you live among them), but to inspire you to hang in there until we can again. I hunger to return to them, but at least I can see them whenever I walk outside.