Oakland Geology

Oakland was visited soon after the missionaries of New Spain established their capital port city at Monterey, in 1769. The area’s unusual terrain gave them trouble, and part of the reason was the set of treeless hills of sand and gravel in its midsection that I call the Fan. The Fan interrupts the nice clean plain that otherwise extends the whole East Bay. Here’s how it looks in a digital elevation model and the geologic map. (As always, click to enlarge.)

The first Europeans to have stood where Oakland sits were four scouts under the leadership of Spanish-born army captain Pedro Fages, who came from Monterey to the East Bay in November of 1770 with a party of six soldiers and a muleteer. It was a short reconnaissance visit that Fages, a seasoned leader who earlier that year had been left in charge of Alta California, made on his own initiative.

In the first part of his trip, Fages pioneered the route inland from Monterey that is traced today by U.S. 101. He then made his way up the East Bay, making camp at San Lorenzo Creek in present-day Hayward, near where scouts from the Portola expedition had apparently stopped the previous year. Fages’ notes are vague; this is the entire record of the day:

November 28. — Four soldiers set out to explore the country, and at night returned saying that they had travelled about seven leagues to the north; that the country was very good and level; that they had climbed to the top of a hill but had not been able to see the end of an estuary which lay before them and which communicated with the one which lay at our feet; that they had seen many tracks of cloven hoofs which they thought were of buffalo; that close to the hills which they passed at the right there were some springs of water; and that they had crossed two small streams of it. They said, also, that they had seen the mouth of the estuary, which they thought to be the one which entered through the bay of the port of San Francisco. This I confirm through having seen it.

(Some explanation: The Spanish league is a little over 2-1/2 miles. The “estuary which lay before them” refers to San Pablo Bay and the one “at our feet” refers to San Francisco Bay. The “port of San Francisco” means Drakes Bay, the “bay of the port of San Francisco” is the bight between Point San Pedro and Point Reyes, and the “mouth of the estuary” is the Golden Gate.)

The men apparently hiked a total of about 16 miles, or 8 miles each way, as estimated by walking. If that whole route was “very good and level” ground, they must have stayed on the flats, and they must not have reached San Antonio Slough (present-day Lake Merritt), which they would have noted because it blocks the way pretty definitively. They were passing the hills overlooking San Leandro and the lower hills of the Fan “at the right” and crossed “two small streams.” These would have been San Leandro and Sausal Creeks, at their lowest flow early in the rainy season.

The hill they climbed, I think, was the hill of San Antonio Park: it was near where they must have turned back, and from its top can be glimpsed parts of San Pablo Bay and the gap of the Golden Gate, although the actual water passage is not visible. Fages “confirmed” the sighting because he could see the gap, though less clearly, from where he spent the day in Hayward. The presence of the Golden Gate was known from the 1734 voyage of Cabrera Bueno, but it had not yet been charted. Here’s the inferred route.

And on the Bache map of 1857 I show the hill’s location with an X. At that time it was a lookout station for the Brooklyn harbor; today it’s a park that still has good views.

And here’s the topography in detail.

Fages returned in the spring of 1772 to push farther north. This time it was a proper expedition that included 12 soldiers, a muleteer, an Indian guide and a priest, Juan Crespi, whose diary served as a formal record. Their primary goal was to fix the position of the Golden Gate in preparation for founding the San Francisco mission; secondarily they sought to find a way around San Pablo Bay. Oakland, with the hilly maze of the Fan and the inconvenient slough in its midst, was in the way.

Leaving the familiar campsite in Hayward on 26 March, they hiked four leagues. Crespi recorded that they crossed five creeks, “three of them medium-sized and two very large, their banks grown with alders, cottonwoods, live oaks, and some laurels.” By my count these would be San Leandro Creek (large), Arroyo Viejo (small), Lion Creek (small), Peralta Creek (small) and Sausal Creek (large).

At the end of four leagues we halted not very far from an arm of the estuary [Oakland Estuary/San Antonio Creek], which forms with another [San Leandro Bay] something of a peninsula [Alameda], where there is a grove of live oaks, which one can enter only from the mainland side. The camping place is about four leagues from the principal estuary or arm of the sea, which we made out from this place very well, and it looks like a sea to us.

I place the camp’s location near Foothill Boulevard west of Sausal Creek and not, as others have done, up near Mills College. Crespi observed, “The site is very suitable for a good settlement; for on account of the proximity of the forest they could provide themselves with timber and firewood. This place was called Arroyo del Bosque.”

The next day they set out early heading north-northwest, but then ran into the wide tidal channel of Lake Merritt: “Because of the estuary [San Antonio Slough] which surrounds the wood [Alameda] and penetrates into the land about four or five leagues until it heads in a mountain range, we were compelled to travel about a league and a half by some ranges of hills, which, although they are all treeless and grass-covered, annoyed us very much with their ascents and descents.”

This part of town is still up and down. The land seen by the Fages party differed from modern Oakland in that the creeks feeding Lake Merritt — Indian Gulch, Wildwood and Pleasant Valley Creeks — were not culverted and paved over with nice asphalt streets, but wide marshy tracts extending well away from the Lake, especially at this time of year. The detours were surely tedious. The mosquitoes, too, drove them all nuts.

After three leagues of trudging they came out on the other side of the Fan. My idea of their route was up Grand Avenue, over the ridge at Linda Avenue, across the valley of Glen Echo Creek and over the last low ridge of the Fan on 41st Street. At this point the party “entered an immense plain,” and they saw for the first time the Golden Gate itself.

They stopped for a while to observe it closely, and Crespi noted its features accurately. We can approximate this view today from the crest of 40th Street Way. They went on to the northwest that day for another league and into history, leaving the territory of Oakland on good terms. They didn’t return this way but instead walked up toward the Delta and looped back south through present-day Walnut Creek and Pleasanton. The next visitors to Oakland were the Anza party in 1776.

DEM images from the National Map site, route maps from gmap-pedometer.com

This entry was posted on 4 January 2021 at 8:01 am and is filed under Other topics, the Fan. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.