Pryal’s gold mine

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.

7 Responses to “Pryal’s gold mine”

  1. robinwells3 Says:

    Happy New Year. Just want you to know that while I never comment, I read all your posts with great interest. So very well done.

  2. J. Christian Says:

    A few years ago I tried to track down the jewelry store in north Berkeley that displayed a piece of gold in quartz from north Berkeley. The current occupant knew of the store which had closed; one owner was still alive. Would love to see a piece of Berkeley gold.

    I wonder if the same event that enriched the rhyolites of north Berkeley with mercury might have deposited some gold too.

  3. Charlotte Steinzig Says:

    I grew up on Pryal in the early 1950’s until the demolishing of our home for highway 24, alas. I’ll be forwarding this terrific piece onto my siblings. Many thanks, as always.

  4. Anne Says:

    Thank you Andrew for this interesting piece on something other than the news. I hope you’ll be leading walks again someday soon.

  5. ealdredsca Says:

    Interesting article. I was sidetracked into trying to find pictures of the current dam and spillway. In the first photo, it looks like the spillway is undergoing uncontrolled erosion. I also thought the land slump into the lake right there was rather unpromising as well. :) Amusingly, when searching for Lake Temescal dam on Google it came up with your post entitled “Two Dams” from June 1, 2009.

    I see your posts via California Geology Forum on Facebook and always enjoy reading them.

  6. Jack Lamb Says:

    Very cool article – a tricky spot no doubt, with the damming of lake Temescal and the later construction of the Sacramento Northern Railway through that unit. I wonder if there are geological reports surviving from either project. Out of curiosity, where did you read about the other accounts of gold?
    Cheers,
    Jack

  7. Andrew Alden Says:

    The Berkeley Hills example is somewhere in my sources. Here are my notes for gold in Leona Heights:

    Alameda Argus 19 July 1898 (www.newspapers.com/image/606994760/) – “Fritz Boehmer was exhibiting to friends this morning a small quartz specimen, rich in gold, which was secured by him from a prospector who says it came from the hills near Leona Heights.” Tribune 20 Jul 1898 (www.newspapers.com/image/72312745/) – “Fritz Boehmer of Alameda declares that there is gold in the hills near Leona Heights and in proof of his assertion exhibits a small piece of quartz rich in gold. His explorations have resulted in the discovery of extensive quarries of blue trap rock, enough to pave all the roadways of the Pacific Coast.” Argus 22 Jul 1989 (www.newspapers.com/image/606994872/) – more extensive account, still no firm ID of gold. Quote, “I do not personally care to develop any mining property, as I never have any more luck. . . . I am more interested in mining for springs.”

Leave a reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s


%d bloggers like this: