Murieta Rock, El Cerrito

In Gold Rush days, the Bay area was as wild as the rest of California: depopulated of Indigenous people and a free-for-all of frontier characters. One of those characters was the legendary outlaw Joaquin Murieta. His story, at least the version we have today, had all the makings of legend — a handsome, peaceable Mexican, viciously victimized along with his wife and family at the hands of Americans, who turned desperado and came to a bad end. As befits a good legend, every crime in California was added to his name — and this fine outcrop too in the hills of northern El Cerrito.

The rock stands out in early photos of El Cerrito, back when the hills were still bare, but today it’s unobtrusive in surroundings of trees and homes at the intersection of Cutting and Arlington Boulevards. It’s also smaller than it used to be; a rectangular quarry pit has been carved into its southwestern side.

Supposedly Murieta’s gang would watch the main road from up here and swoop down on victims. Or this would be their lookout when they hid out in Wildcat Canyon. That may have been. I think the name stuck because it looks like a broken-down haunted house made of a rare, unearthly-looking blueschist.

The area is geologically interesting. The rock is just south of Cutting, below the large “L” at the center (part of the name of the old San Pablo rancho).

All the bluish rocks are Franciscan, the orange (Tor) is the much younger Orinda Formation, and between them is the Hayward fault zone. “KJfy” is a metamorphosed sandstone and “spm” is the melange. Regular readers may recognize “Jsv” as the Leona volcanics, but this little pod is actually the northernmost occurrence of Northbrae rhyolite, the stuff of Berkeley’s rock parks. (Thanks to Karl in the comments for flagging my oversight.)

Murieta Rock is a high-grade block in a melange of serpentinite — a rare outcrop within a rare setting — and for background I refer you to this post from the last time I was up this way. Notice the large areas of the map labeled “Qls”; these are gigantic, slow landslides all of which originate in that melange. More of them are in north Berkeley (see my 2017 walking guide to the area, from the Berkeley Path Wanderers Association site).

Enough of that. You can reach Murieta Rock on the 7 bus line, from either the El Cerrito del Norte or Downtown Berkeley BART stations, or drive there yourself of course, but I enjoyed walking there through Canyon Trail Park — if I were Murieta, I’d swoop that way to carry out my robberies. The view from the top of the rock over San Pablo Bay is superb.

And since this is Valentines Day, why not consider the rock for a romantic geo-outing?

13 Responses to “Murieta Rock, El Cerrito”

  1. Karl Hans Says:

    Last year after I commented on the age of the “Madera School rhyolite” in the El Cerrito Hills, mapped by Wakabyashi and Rowe (2015) as “Miocene Northbrae Rhyolite”, I went to search for anything more I could find that Lin Murphy might have published. It turns out that it appears her Masters thesis at Cal State Hayward was on a different subject than the silica rich rocks of the Berkeley Hills and it does not appear that her data were published as a thesis or in a journal.

    However I did find a 2003 publication (see below) on the subject by Lin Murphy at the UC Berkeley Earth Sciences library that provides a single statement that sheds a little light on the EC Madera Rhyolite designation as Northbrae. She notes “occasional flowbanding identifies it as Northbrae rather than Leona”.

    I have been curious about this because the Madera Rhyolite looks more like how she describes Leona Rhyolite as “fractured, weathered, crumbling”, than the type of rhyolite you find around the Indian Rock neighborhood. In the 2021 NCGS “Walking Guide to the Geology of the Hillside Natural Area and Hayward Fault, East Bay Hills, El Cerrito CA” August 14 , 2021, Gary Prost, William E. Motzer and Mark Petrofsky, there a short note about the rhyolite: “Some recent workers believe this is a welded tuff rather than a rhyolite flow”.

    So it looks like a subject for further investigation.

    The upcoming El Cerrito Hillside Festival this coming weekend will include a geology walk on Saturday May 6 and perhaps an opportunity to discuss these findings:

    SaturdayMay 6, 2023 1 to 3:30 p.m. Geology Walk.Co-sponsored by theNorthern California Geological Society. Leaders are geologist Gary Prost, Mark Petrofsky, a former teacher and Bill Motzer, a geologist/geo-chemist. Learn about the geological setting of El Cerrito, rocks, faults and landslides. This moderate to strenuous walk has steep sections.Location Five, Schmidt Lane Trailhead.

    For more information and a full schedule of the Hillside Festival go to

    Below are some excerpts from the two Murphy publications I have found including a finding of the Northbrae age being 11.5 million year U-Pb age. Leona on other hand is generally described as late Jurrasic although I do not have a specific reference regarding analysis to date that rhyolite.

    Silica-rich Volcanics of the Berkeley Hills Lin Murphy June 21, 2001
    (found on the internet long ago, does not seem to be available anymore)
    In outcrop, the Leona is fractured, weathered, crumbling. It has defied definitive analysis because it lacks distinctive textures and is very altered. In contrast, the Northbrae, which crops out at Indian Rock and Great Stone Face Parks and in adjacent neighborhoods, forms coherent prominences. In contrast with the generally featureless and massive Leona, Northbrae Rhyolite at Indian Rock and Great Stone Face Parks is flow-banded and contains autobrecciated flow-banded and nonflow-banded clasts, suggesting origin as a lava flow or dome. We have distinguished the flow-bandedNorthbrae rhyolite chemically from the nonflow-banded Leona Rhyolite rocks at Alvarado Park and Tunnel Road by the former’s greater K2O content, as well by trace element discrimination diagrams.

    Field Guide to Silica-Rich Rocks in the Berkeley Hills Lin Murphy 2003
    (UC Berkeley Earth Sciences Library QE 445 C3 M87 2003 C.2 EART)

    The Northbrae Rhyolite is areally limited to the Northbrae residential subdivision, north of the University of California campus. Outcrops are all clustered within ½ mile of Indian Rock Park, with the exception of Madera School, ~2 ¾ miles north of Indian Rock. The Madera School exposure has been greatly diminished in size since 1980: only occasional flowbanding identifies it as Northbrae, rather than Leona.

    In Spring 2002, Fleck and Wooden of the USGS, Menlo Park, dated zircons from two different outcrops of the Northbrae Rhyolite. Their data indicate that the Northbrae Rhyolite is a newly recognized unit of the Cenozoic volcanics that erupted in the wake of the northwestward- migrating Mendocino triple junction.These Cenozoic volcanics are believed to be the result of the “asthenospheric window” (McLaughlin. 1996) or “slab gap” (Dickinson, 1997) that developed from the interaction of the East Pacific Rise and the Farallon trench. Similar radiometric ages suggest that the Quien Sabe, north of Hollister, and the Northbrae in Berkeley are part of the same volcanic field.

    Murphy, Fleck, and Wooden. 2002. The Northbrae Rhyolite in the Berkeley Hills: A Rock Well- Misunderstood. Reports 11.5 million-year U-Pb age of Northbrae Rhyolite, which indicates that it is a heretofore unrecognized volcanic that erupted in the wake of the northward-migrating Mendocino Triple Junction.

  2. Mark Petrof Says:

    What is the age of the Leona Volcanics? How far in time are the separated from the Late Miocene Rhyolite?

  3. Andrew Alden Says:

    Far as I know, the actual data haven’t been published in a peer-reviewed paper. They were presented at a poster session of the 2002 GSA annual meeting; abstract here. Although the abstract does not include the date of 11.5 Ma, that is the source that everyone else cites. (Murphy posted a further comment about these rocks in 2009.)

  4. brian O'Regan Says:

    Hi Andrew. Indeed the “Jsv” designation in Berkeley is now the Northbrae Rhyolite, or whatever it’s official name is. But still, one would not, I think, expect blueschist to be mixed with the rhyolite. But there it is. That’s the joy of living somewhere so complicated.
    On a related note, I’ve been unable to find where the Lin Murphy age data on the Northbrae Rhyolite was published. I’ve found some conference abstracts, but the all seem to be labelled “withdrawn”. Do you know where this data is to be found?

  5. Andrew Alden Says:

    Brian, that area of Jsv has been clarified since publication of Graymer’s map, as earlier comments have noted. It’s a true rhyolite of late Miocene age and not at all the same thing as the Leona Volcanics.

    That part of Berkeley is a mess, and geologic maps are always a simplification.

  6. Mark Petrof Says:

    Slide zone? The ridge from Kensington to East Richmond Heights is very high grade blueschist. I’m going to have to get Wakabayashi to comment on it.

  7. brian O'Regan Says:

    For anyone who is following Andrew’s trail of blueschist, there is a unique opportunity today tomorrow and next Saturday. There is an open house at 1106 Oxford Ave, Berkeley, where there is an interesting chunk of rock in the back yard. It’s mostly underground, and way too big for human movement. It looks like blueschist to me, although it is not highly schistose. It’s in a swale, and gives the impression of “bedrock”. The problem is, the area is mapped by Graymer as Jsv, in which one would not expect blueschist. The outcrop is just beyond the north edge of the slide area mapped by Kropp or by satellite. If it is a slide knocker, where did it come from up above? If you go to look at it. Also peer into the backyard of 1000 Mariposa, two blocks west, where there is a much bigger exposure of what I think is the same stuff. I’m tempted to say it’s part of the melange, and the Graymer map is wrong for this area, but …

  8. Robert Conser Says:

    My grandparents had a home at the corner of Languinitas and ??. Just below the country club. At the time, this rock was referred to as chimney rock, as one of the neighbors blasted it and used the beautiful pieces to build their chimney. This was probably in the early 1900’s.
    Rummer has it that Joaquin Murrieta and his gang used this look out to spot approaching vigilantes.
    Having climbed up there as a child, I can only imagine the view that was afforded before the demolition (and smog)

  9. Yan Biomil Says:

    Thank you for the interesting story. What is the difference in appearance between blueschist and serpentine ( which, I am told,is the California state rock) ?

  10. Mitzy Valdes Says:

    great informative stuff

  11. Andrew Alden Says:

    Thanks, Karl. I should’ve checked Wakabayashi’s mapping and gotten the rhyolite right. (The paper has a coauthor, Christie Rowe of McGill University.) The geologic map I use (see its page on this site) was published in 2000, before the correct identity of the Northbrae rhyolite was widely known. I haven’t seen those particular exposures in person yet. The nomenclature of the Franciscan is a mess and not worth the attention of most readers. Albany Hill is simply one lump of the dismembered Novato Quarry terrane. “Knockers” are large blocks in the melange that protrude from the ground; I’ve retired this old field term because some men think it’s funny and have embarrassed their women peers.

  12. Karl Hans Says:

    A response and a comment based on Wakabyashi’s 2015 International Geology Review article (V57 No 5-8) “Wither the Megathrust: Localization of a large scale subduction slip along contact of a melange:

    Wakabayashi identifies the light blue as Angel Island Nappe (blueschist facies graywacke). Above this nappe and extending to the Hayward Fault, the Tiburon melange contains high grade blueschist and serpentine rocks readily seen along the Arlington.

    Regarding the rhyolite, it is apparently younger Northbrae rather than older Leona, based on lin Murphy’s evaluation. Wakabayashi writes:
    “Rhyolitic volcanic rocks unconformably overlie the Franciscan rocks. These have been mismapped in the past as Jurrassic rocks of the Coast Range Ophiolote but detailed field studies and geochemical and geochronological analysis have shown similar rocks to be Miocene postdating Franciscan subduction.”

    He maps them as “Miocene Northbrae Rhyolite”.

    The exact origin of the Northbrae rhyolite (indian rock and others) has not yet been determined as I inderstand, and there there might be some association with Quien Sabe formation to the south.

    Regarding Albany Hill, it is mapped as part of the Novato Quarry Terrane, extending north west through Point Richmond, Red Rock, China Camp and into Novato. So not what would be considered a “knocker”, but what makes it so prominent and subject to less erosive trimming has not been explained to me.

  13. mpetrof Says:

    What is the light blue between the serpentine melange (spr?) and the Orinda (Tor)? The whole ridge and back in to Wildcat R.P. is rife with high grade blueschist. I gather that much of the KJfy is blueschist fascies (just to confuse matters via confusing terminology). Or is the lower grade blueschist fascies of the quarry to the south also in the light blue?

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