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Lobe 5 of the Fan: Coolidge

10 July 2023

It’s been a while since I made a close inspection of the Fan, which is the name I gave to the wide fringe of gravel hills that surrounds the Piedmont bedrock block. I’ve not just given the Fan a name, but also have assigned numbers to its different parts, as seen in this piece of the Oakland geologic map.

Today’s post is about lobe number 5, the Coolidge lobe. I’m giving it this name because Coolidge Avenue runs from its westernmost tip up its entire length. All parts of it make interesting walking.

This is where the first non-Indigenous building in Oakland’s territory was constructed in 1821, an adobe dwelling on Luís María Peralta’s royal land grant. Spanish/Mexican adobes were what inspired the “ranch-style house.” In fact, Coolidge Avenue was originally named Peralta Avenue (Oakland annexed the area in 1909 and renamed it to avoid confusion with Peralta Street in West Oakland). The ranch site is preserved today at Peralta Hacienda Historical Park. It’s possible to explore lobe 5 and appreciate why this particular site attracted Peralta.

Lobe 5 is a triangle defined by the floodplains of Sausal Creek and Peralta Creek and the bedrock of the Piedmont block. It happens to reach a higher elevation than any other lobe, over 300 feet. Here’s a closeup of the geologic map, showing the Fan’s ancient gravel as the orange unit labeled “Qpaf” (Quaternary (Pleistocene) alluvial fan and alluvium deposits).

There’s a strip of a unit labeled “Qpoaf” signifying slightly older deposits of the same type. I give this limited credence because its description is exactly the same as the other unit; I think it was mapped this way based on the topography.

I said Peralta Creek defines the edge of the lobe but in fact it cuts across it, assuming one accepts the mapping and I have no reason not to. The creek has to flow this way because it’s confined by Rettig canyon, a water gap in the bedrock ridge at the top. The digital elevation model will make this clearer I hope.

The Hayward fault runs through that slashing valley above the canyon; I described it in this post a few years ago. That means the creeks here have had a complicated history as the fault kept ripping up their headwaters and raising and lowering land. That’s a discussion for another post.

The lobe itself has a corrugated surface, a set of grooves that coalesce down near the tip of the lobe. Those are little stream valleys, which show up on the early Oakland maps as running creeks. This map is from 1884.


Peralta Creek at center, Sausal Creek at left, Courtland Creek at right. (Source)

This odd stream pattern is more evidence of an odd history, one of the puzzles posed by the Allendale flat. More practically, the lobe had a good supply of water.

Here’s a view across the middle one of these creek valleys, looking south on Delaware Street just above the freeway. (The image at the end of this post has locations of all photos.)

The edges of the Coolidge lobe are quite distinct. On the Fruitvale side, here’s the edge as seen from below on Coloma Street.

Looking down from the lobe across the Sausal Creek floodplain at E. 27th Street.

The east side of the lobe is less abrupt, but Peralta Creek cuts quite a notch through its upper end. This is the creek bed where it interrupts California Street, above the freeway.

Access is difficult, but the stream banks in this vicinity expose the material of the Fan. It’s a clayey gravel with cobbles of the Leona volcanics and other rocks from the high hills.

It’s fairly well indurated. The stream is lined with huge eucalyptus trees, easily visible from the hills and on Google Maps. I think these pose a greater risk to the neighbors than the tall exposures of this alluvium.

Here’s the eastern edge of the lobe looking down onto the Allendale flat from Salisbury Street, a block toward the Bay from Peralta Hacienda Park near the lobe’s tip.

The hacienda site was well situated in 1821. All of the surroundings was grassland, except probably some oaks and laurels along the creek, and the creek, with its essential water supply, was easily reached without high banks.

The site commanded good views of both the Peralta and Sausal Creek floodplains as well as the Bay. You can still glimpse them here if you peek between the trees and buildings as you walk around. Its location, slightly over the crest of the lobe, offered some shelter from strong Bay breezes. There was good soil for manufacturing adobe bricks and to support the kitchen garden. Presumably there were good Ohlone trails through the area. A decent landing, just half a league away to the west at the mouth of 14th Avenue Creek, served the ranch’s needs for shipping. That’s where the East Bay’s earliest secular settlement took root in the 1840s, named San Antonio and then Brooklyn.

Here are the photo locations.

Posted in Oakland geology puzzles, the Fan | 3 Comments »

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.

Posted in Oakland geology views, the Fan | 2 Comments »

Anza and the Fan

18 January 2021

After Pedro Fages came through the East Bay in 1770 and 1772, no one from New Spain appears to have visited the land on which Oakland sits until Juan Bautista de Anza led an exploring expedition here in the spring of 1776. Scholars seem to be quite sure of where the group went, but when I examine the record I find more and more room for interpretation and inference.

I’m not going to pretend I’ve examined the manuscripts or know 18th-century Spanish. I’ve accessed translations of those manuscripts and, well, here’s some of the questionable things and wiggle room I see in the record.

  • Neither Anza nor the group’s diarist, Father Pedro Font, had been with Fages in the earlier visits, so they had only Fages’s records to compare against the countryside they saw. We can’t rely on their interpretation, especially as it appears they took a different route than Fages.
  • We can’t rely on their directions. The East Bay from Berkeley south is persistently slanted 33 degrees west of north (thanks to the Hayward fault and the plate boundary of which it’s part) making it hard to eyeball true directions; magnetic north was apparently 12 degrees east of true north at the time (thanks, NOAA); and Font complained about the poor quality of his compass, so the explorers’ impressions are suspect. The men were not experienced sailors either, people I might trust, but army soldiers. Moreover, I wonder about the transcriptions. There seem to be too many instances of “northwest” (noroeste) and not enough of “northeast” (noreste) to fit the written route on modern maps. And the scholars, whom I trust on this topic, point out that very discrepancy between different copies of these documents, all of which were made by hand.
  • We can’t rely on their distances. No one had odometers. Font did his best, prefacing his notes with a discussion of the length of the Spanish league (approximately 2.6 miles, apparently), but even so the men were on horseback whereas Fages had been on foot. On the day they came through Oakland, Anza wrote down that they went “about ten leagues” while Font put it at “some fourteen leagues.” The day’s ride was long, from Hayward to Pinole, and the group was in a hurry, with their goal still ahead of them. (And just as Fages had complained in 1772, the Anza party was beset with mosquitoes all that day.)

Long story short, I think that whereas Fages mostly skirted the Fan as he sought (and failed to find) an easy level route through Oakland, Anza rode pretty straight through it.

Anza’s group set out from their camp on San Lorenzo Creek, in present-day Hayward, that morning at 7 and rode along the foot of the hills, with a jog upstream to get across the deep arroyo of San Leandro Creek, and then on to the edge of the Fan, the hill of Pleistocene gravel occupied by Evergreen Cemetery, in the lower right corner of this digital elevation model.

Where Fages turned left to stay on the flats, Anza headed the horses straight, toward a promising gap in the hills,

and into the Allendale flat. Almost fifty years later, Luís Maria Peralta’s family would put the first hacienda on their huge East Bay land grant there, just across Peralta Creek. “About two leagues” after crossing San Leandro Creek into Oakland territory, Font wrote that they “crossed a small arroyo without water and almost without trees,” which I think was Peralta Creek. “Then a little further on we ascended a hill which is on a straight line with the mainland and the plain which runs toward a very thick grove of oaks and live oaks on the banks of the estuary,” where he sketched the view toward the Golden Gate. That is this drawing, showing the Alameda peninsula flanked by San Leandro Bay on the left and the Estuary on the right:

In my interpretation, he would have been sitting on the ridge where Patten University sits today but higher up, maybe where Lincoln Avenue starts today. It also could have been down on Carrington hill; both ridges line up with the Alameda peninsula, which was a large encinal (live-oak grove) at the time.

“Then, descending the hill, we crossed another arroyo almost without trees and with some little pools of water which did not run. This appears to be the arroyo which Father Crespi called the Arroyo del Bosque and which empties into the extremity of one arm of the estuary.” He refers to Sausal Creek as described by the Fages party in 1772.

“We continued the journey over hills and plains, crossing two more arroyos with little water, deep beds, and a heavy growth of trees, the second one having more than the other, and both of them flowing into a bay which the arm of the estuary forms on this side.” These I interpret as Indian Gulch and Pleasant Valley Creeks, which clearly both drain into Lake Merritt, which was then a narrow inlet with wide mudflats. I don’t think the group went near the Lake but instead were higher up the valleys — they were on horseback, after all.

“Afterward we entered a plain in which we crossed two small arroyos without water.” Finally they had left the hills of the Fan and were back on the East Bay plain. That would make these two streams Temescal and Strawberry Creeks. “From this plain we clearly descried the mouth of the port, and when the point of the red cliff on the inside was in line with the outer point of the mouth, I observed the direction in which they ran, and saw that it was to the west with some declination to the south.” That matches the view of the Golden Gate as seen from Berkeley.

Oakland remained something of a distant place until the San Francisco and San Jose missions had captured or driven off the native people and established their own purposes on the territory: food and fodder cultivation in the Richmond area and cattle range in the flats from Fremont to East Oakland.

I want to note that Fages and Anza did not come as conquerors. Their assignment, at the dawn of Alta California, was to establish friendly relations with the natives. They exchanged gifts with every group they met: glass beads, generally; and a surprising number of native groups gave them duck decoys in addition to food. The situation did not last. The priests could not even perceive the fine-tuned ecosystem in which the Ohlone were the keystone species, only naked children of nature who must be trained in their own god’s image.

Posted in Other topics, the Fan | 4 Comments »

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