Oakland Geology

The Gold Rush was a bust everywhere in the Oakland Hills, with one exception. That was a short-lived mine, started in 1864, on A. D. Pryal’s ranch in the northern Rockridge neighborhood. This seems most unlikely at first blush, but the source is Titus Fay Cronise’s unimpeachable book The Natural Wealth of California (1868):

“In 1864, Mr. A. D. Pryal, owner of a large ranch about four miles east from Oakland, discovered a vein of auriferous quartz in the Contra Costa hills, which cross his lands. Some of the specimens from this vein were rich in free gold, and the mine opened under the name Temescal, paid well for a short time, but the dislocation of the strata, a little below the surface, rendered its further working unprofitable.”

The only remotely likely source for such an ore is a small body of highly altered mantle material, called silica-carbonate rock (also called listwanite or listvenite), that was caught up in the Hayward Fault. Long-time readers may recall a post of mine on the subject that involved this same locality. Here’s what the area looks like on the geologic map.

That’s College Avenue running up the left side and Route 24 in purple running along the bottom, with Chabot Road to its immediate north; Lake Temescal is in the corner and the silica-carbonate is the dark blue wedge just north of it between strands of the Hayward fault. When I explored it nine years ago, I bushwhacked up its western edge and found nothing. This weekend, I bushwhacked up its eastern edge.

This part of town has been heavily built upon since Pryal first dug it up, but old photos from (I think) the 1890s show the possibilities. The first shows the Lake Temescal dam and the creek below the spillway. What would’ve been the continuation of Chabot Road (then known as Pryal Lane) runs in front of the white house at the left. The little bridge at the bottom is where the next photo is.

Notice what a mess the hillside is above the dam. Anthony Chabot apparently sluiced it all into the reservoir when he built the dam in 1868. And notice what an erosional mess the streambed is. Nobody cared back then, or nobody downstream cared enough to sue Chabot.

^{Photos courtesy Bancroft Library via Online Archive of California}

What caught my eye was the boulder at center left. Well, first, the streambank behind it looks like fault gouge, the pale powdery dirt that faults make by grinding rocks (and which I documented down at the London Road landslide). Anyway, the boulder at center left looks just like a big slickenside, the scraped-and-buffed surface that faults make by rubbing rocks.

The gist of all this is that a wide, complex fault zone like the geologic map shows could very easily carry slivers of rock from quite far away. And this is little known today, but in the early days there were curious, isolated reports of stones of gold-bearing quartz in our hills. At least two have popped up in my reading, one from north Berkeley and another from Leona Heights. So my hopes were not high as I set out on this traverse, but they weren’t zero either.

It was a real nice day. The streams had water and the ground was pretty firm and quiet. This is looking down at the head of Chabot Road, which was truncated by the freeway long ago. A strand of the fault is mapped there, but the road shows no sign of it.

I found bedrock this time. One bit was deeply weathered Leona volcanics, the same stuff that crops out uphill to the east (pink on the map).

This outcrop looked more like a strongly sheared and altered basalt, not unexpected in the Leona volcanics.

This outcrop, hard to tell; probably more of the same, brecciated.

None of what I saw appeared to be silica-carbonate rock or even leaning in that direction. But that’s what I would expect 160 years after a minor gold find petered out. I’m still not clear on what evidence led the mappers to think such a thing was here at all.

Besides, I was happy to find real bedrock at all during this visit, and there’s still a bit of the territory I haven’t set foot on yet — something for another day. After a long absence from the field, these rocks all looked beautiful to me anyway.

Starting on 8 June 1871, an ad in the Oakland Daily Transcript touted “White Quartz Gravel / for Sidewalks, Garden Walks, and Carriage Drives, It Makes A Beautiful And Solid Walk!” and offered this recommendation:

“Mayor N. W. Spaulding, in his recent message to the City Council, said: ‘The only macadam walks which have so far proved successful have been made from [the Fowler quarry or] the white cement gravel found in the vicinity of Fruit Vale. The latter appears to be preferable because it becomes more solidified than any other material heretofore used, being less affected by the agencies of the weather. It has been used in some localities in this city for the last eighteen months. The peculiarities which recommend this cement gravel are: that when it is exposed to the elements it becomes adhesive and firm, is comparatively free from mud in Winter and dust in Summer. This makes it a complete and permanent improvement. Sidewalks made from this material are estimated to cost about 35 cents per lineal foot for walks eighteen feet wide.’ The subscriber has now got his road through to the White Cement Gravel Quarry, and will furnish at short notice any amount of Gravel for the above purposes, by leaving orders at Gardiner & Hunt’s office, Broadway, between Eighth and Ninth Sts., Oakland, and at the Brooklyn Postoffice.”

It was signed “L. Reichert, Fruit Vale.”

This material seems quite out of place for Oakland, and its properties appear unlikely too. But I’ve tracked it to land that Reichert owned above the Dimond district, at the end of today’s Maple Avenue, where a “gravel bank” is noted on the 1878 Thompson & West map.

And we’ve been here! It’s in the land south of the LDS Temple that was ruined by the London Road landslide in 1970. And that explains the peculiarities of the material. It was fault gouge: bedrock crunched into powder by the Hayward fault.

I believe its self-cementing character comes from a significant content of calcium carbonate, which is present both in the Franciscan melange on the downhill side and in the serpentinite a little ways uphill.

Despite the mayor’s endorsement, business for the Fruit Vale Quartz Company seemed to be spotty. Business broker Andrew Baird, of San Francisco, took over for a short time in 1873 under his own name; then Reichert sold the “inexhaustible” gravel pit, and the 25-acre parcel it sat on, in July 1873 to Elias L. Beard, a prominent wheeler-dealer based in Mission San Jose. Beard is shown as the owner in later maps (misspelled Baird, probably because the adjoining parcel was owned by Julia C. Baird). The 1874 city directory lists L. Reichert Jr. as a teamster with the Fruit Vale Quartz Company — perhaps the founder’s son.

Baird tried again to sell the parcel in 1875, 1876 and 1878, the year that Beard went bankrupt and lost almost everything.

I have little idea what happened after that, except that the State Bureau of Mines annual report 38, published in 1906, recorded this as the “Packard Quarry,” of which the newspapers make no mention. And as of 1912, the land was in the hands of the Realty Syndicate, part of its enormous hillside empire. A decade later the land began to undergo the process of residential subdivision that endures to this day.