Geology answers for Montecito and Santa Barbara

Just before it started, the geology meeting at the Santa Barbara Central Library on Thursday looked like this from the front of the room (where I also tweeted the same pano):

Geologist Ed Keller

Our speakers were geology professor Ed Keller of UCSB and Engineering Geologist Larry Gurrola, who also works and studies with Ed. That’s Ed in the shot below.

As a geology freak, I know how easily terms like “debris flow,” “fanglomerate” and “alluvial fan” can clear a room. But this gig was SRO. That’s because around 3:15 in the morning of January 9th, debris flowed out of canyons and deposited fresh fanglomerate across the alluvial fan that comprises most of Montecito, destroying (by my count on the map below) 178 buildings, damaging more than twice that many, and killing 23 people. Two of those—a 2 year old girl and a 17 year old boy—are still interred in the fresh fanglomerate and sought by cadaver dogs.* The whole thing is beyond sad and awful.

The town was evacuated after the disaster so rescue and recovery work could proceed without interference, and infrastructure could be found and repaired: a job that required removing twenty thousand truckloads of mud and rocks. That work continues while evacuation orders are gradually lifted, allowing the town to repopulate itself to the very limited degree it can.

I talked today with a friend whose business is cleaning houses. Besides grieving the dead, some of whom were friends or customers, she reports that the cleaning work is some of the most difficult she has ever faced, even in homes that were spared the mud and rocks. Refrigerators and freezers, sitting closed and without electricity for weeks, reek of death and rot. Other customers won’t be back because their houses are gone.

Highway 101, one of just two freeways connecting Northern and Southern California, runs through town near the coast and more than two miles from the mountain front. Three debris flows converged on the highway and used it as a catch basin, filling its deep parts to the height of at least one bridge before spilling over its far side and continuing to the edge of the sea. It took two weeks of constant excavation and repair work before traffic could move again. Most exits remain closed. Coast Village Road, Montecito’s Main Street, is open for employees of stores there, but little is open for customers yet, since infrastructural graces such as water are not fully restored. (I saw the Honor Bar operating with its own water tank, and a water truck nearby.) Opening Upper Village will take longer. Some landmark institutions, such as San Ysidro Ranch and La Casa Santa Maria, will take years to restore. (From what I gather, San Ysidro Ranch, arguably the nicest hotel in the world, was nearly destroyed. Its website thank firefighters for salvation from the Thomas Fire. But nothing, I gather, could have save it from the huge debris flow wiped out nearly everything on the flanks of San Ysidro Creek. (All the top red dots along San Ysidro Creek in the map below mark lost buildings at the Ranch.)

Here is a map with final damage assessments. I’ve augmented it with labels for the canyons and creeks (with one exception: a parallel creek west of Toro Canyon Creek):

Click on the map for a closer view, or click here to view the original. On that one you can click on every dot and read details about it.

I should pause to note that Montecito is no ordinary town. Demographically, it’s Beverly Hills draped over a prettier landscape and attractive to people who would rather not live in Beverly Hills. (In fact the number of notable persons Wikipedia lists for Montecito outnumbers those it lists for Beverly Hills by a score of 77 to 71.) Culturally, it’s a village. Last Monday in The New Yorker, one of those notable villagers, T.Coraghessan Boyle, unpacked some other differences:

I moved here twenty-five years ago, attracted by the natural beauty and semirural ambience, the short walk to the beach and the Lower Village, and the enveloping views of the Santa Ynez Mountains, which rise abruptly from the coastal plain to hold the community in a stony embrace. We have no sidewalks here, if you except the business districts of the Upper and Lower Villages—if we want sidewalks, we can take the five-minute drive into Santa Barbara or, more ambitiously, fight traffic all the way down the coast to Los Angeles. But we don’t want sidewalks. We want nature, we want dirt, trees, flowers, the chaparral that did its best to green the slopes and declivities of the mountains until last month, when the biggest wildfire in California history reduced it all to ash.

Fire is a prerequisite for debris flows, our geologists explained. So is unusually heavy rain in a steep mountain watershed. There are five named canyons, each its own watershed, above Montecito, as we see on the map above. There are more to the east, above Summerland and Carpinteria, the next two towns down the coast. Those towns also took some damage, though less than Montecito.

Ed Keller put up this slide to explain conditions that trigger debris flows, and how they work:

Ed and Larry were emphatic about this: debris flows are not landslides, nor do many start that way (though one did in Rattlesnake Canyon 1100 years ago). They are also not mudslides, so we should stop calling them that. (Though we won’t.)

Debris flows require sloped soils left bare and hydrophobic—resistant to water—after a recent wildfire has burned off the chaparral that normally (as geologists say) “hairs over” the landscape. For a good look at what soil surfaces look like, and are likely to respond to rain, look at the smooth slopes on the uphill side of 101 east of La Conchita. Notice how the surface is not only a smooth brown or gray, but has a crust on it. In a way, the soil surface has turned to glass. That’s why water runs off of it so rapidly.

Wildfires are common, and chaparral is adapted to them, becoming fuel for the next fire as it regenerates and matures. But rainfalls as intense as this one are not common. In just five minutes alone, more than half an inch of rain fell in the steep and funnel-like watersheds above Montecito. This happens about once every few hundred years, or about as often as a tsunami.

It’s hard to generalize about the combination of factors required, but Ed has worked hard to do that, and this slide of his is one way of illustrating how debris flows happen eventually in places like Montecito and Santa Barbara:

From bottom to top, here’s what it says:

  1. Fires happen almost regularly, spreading most widely where chaparral has matured to become abundant fuel, as the firefighters like to call it.
  2. Flood events are more random, given the relative rarity of rain and even more rare rains of “biblical” volume. But they do happen.
  3. Stream beds in the floors of canyons accumulate rocks and boulders that roll down the gradually eroding slopes over time. The depth of these is expressed as basin instablity. Debris flows clear out the rocks and boulders when a big flood event comes right after a fire and basin becomes stable (relatively rock-free) again.
  4. The sediment yield in a flood (F) is maximum when a debris flow (DF) occurs.
  5. Debris flows tend to happen once every few hundred years. And you’re not going to get the big ones if you don’t have the canyon stream bed full of rocks and boulders.

About this set of debris flows in particular:

  1. Destruction down Oak Creek wasn’t as bad as on Montecito, San Ysidro, Buena Vista and Romero Creeks because the canyon feeding it is smaller.
  2. When debris flows hit an obstruction, such as a bridge, they seek out a new bed to flow on. This is one of the actions that creates an alluvial fan. From the map it appears something like that happened—
    1. Where the flow widened when it hit Olive Mill Road, fanning east of Olive Mill to destroy all three blocks between Olive Mill and Santa Elena Lane before taking the Olive Mill bridge across 101 and down to the Biltmore while also helping other flows fill 101 as well. (See Mac’s comment below, and his link to a top map.)
    2. In the area between Buena Vista Creek and its East Fork, which come off different watersheds
    3. Where a debris flow forked south of Mountain Drive after destroying San Ysidro Ranch, continuing down both Randall and El Bosque Roads.

For those who caught (or are about to catch) Ellen’s Facetime with Oprah visiting neighbors, that happened among the red dots at the bottom end of the upper destruction area along San Ysidro Creek, just south of East Valley Road. Oprah’s own place is in the green area beside it on the left, looking a bit like Versailles. (Credit where due, though: Oprah’s was a good and compassionate report.)

Big question: did these debris flows clear out the canyon floors? We (meaning our geologists, sedimentologists, hydrologists and other specialists) won’t know until they trek back into the canyons to see how it all looks. Meanwhile, we do have clues. For example, here are after-and-before photos of Montecito, shot from space. And here is my close-up of the latter, shot one day after the event, when everything was still bare streambeds in the mountains and fresh muck in town:

See the white lines fanning back into the mountains through the canyons (Cold Spring, San Ysidro, Romero, Toro) above Montecito? Ed explained that these appear to be the washed out beds of creeks feeding into those canyons. Here is his slide showing Cold Spring Creek before and after the event:

Looking back at Ed’s basin threshold graphic above, one might say that there isn’t much sediment left for stream beds to yield, and that those in the floors of the canyons have returned to stability, meaning there’s little debris left to flow.

But that photo was of just one spot. There are many miles of creek beds to examine back in those canyons.

Still, one might hope that Montecito has now had its required 200-year event, and a couple more centuries will pass before we have another one.

Ed and Larry caution against such conclusions, emphasizing that most of Montecito’s and Santa Barbara’s inhabited parts gain their existence, beauty or both by grace of debris flows. If your property features boulders, Ed said, a debris flow put them there, and did that not long ago in geologic time.

For an example of boulders as landscape features, here are some we quarried out of our yard more than a decade ago, when we were building a house dug into a hillside:

This is deep in the heart of Santa Barbara.

The matrix mud we now call soil here is likely a mix of Juncal and Cozy Dell shale, Ed explained. Both are poorly lithified silt and erode easily. The boulders are a mix of Matilija and Coldwater sandstone, which comprise the hardest and most vertical parts of the Santa Ynez mountains. The two are so similar that only a trained eye can tell them apart.

All four of those geological formations were established long after dinosaurs vanished. All also accumulated originally as sediments, mostly on ocean floors, probably not far from the equator.

To illustrate one chapter in the story of how those rocks and sediments got here, UCSB has a terrific animation of how the transverse (east-west) Santa Ynez Mountains came to be where they are. Here are three frames in that movie:

What it shows is how, when the Pacific Plate was grinding its way northwest about eighteen million years ago, a hunk of that plate about a hundred miles long and the shape of a bread loaf broke off. At the top end was the future Malibu hills and at the bottom end was the future Point Conception, then situated south of what’s now Tijuana. The future Santa Barbara was west of the future Newport Beach. Then, when the Malibu end of this loaf got jammed at the future Los Angeles, the bottom end of the loaf swept out, clockwise and intact. At the start it was pointing at 5 o’clock and at the end (which isn’t), it pointed at 9:00. This was, and remains, a sideshow off the main event: the continuing crash of the Pacific Plate and the North American one.

Here is an image that helps, from that same link:

Find more geology, with lots of links, in Making sense of what happened to Montecito. I put that post up on the 15th and have been updating it since then. It’s the most popular post in the history of this blog, which I started in 2007. There are also 58 comments, so far.

I’ll be adding more to this post after I visit as much as I can of Montecito (exclusion zones permitting). Meanwhile, I hope this proves useful. Again, corrections and improvements are invited.

30 January

6 April, 2020
*I was told later, by a rescue worker who was on the case, that it was possible that both victims’ bodies had washed all the way to the ocean, and thus will never be found.

In this Edhat story, Ed Keller visits a recently found prior debris flow. An excerpt:

The mud and boulders from a prehistoric debris flow, the second-to-last major flow in Montecito, have been discovered by a UCSB geologist at the Bonnymede condominiums and Hammond’s Meadow, just east of the Coral Casino.

The flow may have occurred between 1,000 and 2,000 years ago, said Ed Keller, a professor of earth science at the university. He’s calling it the “penultimate event.” It came down a channel of Montecito Creek and was likely larger on that creek than during the disaster of Jan. 9, 2018, Keller said. Of 23 people who perished on Jan. 9, 17 died along Montecito Creek.

The long interval between the two events means that the probability of another catastrophic debris flow occurring in Montecito in the next 1,000 years is very low, Keller said.

“It’s reassuring,” he said, “They’re still pretty rare events, if you consider you need a wildfire first and then an intense rainfall. But smaller debris flows could occur, and you could still get a big flash flood. If people are given a warning to evacuate, they should heed it.”

This entry was posted in Future, Geography, Geology, history, infrastructure, Nature, Photography, Places, Research, Santa Barbara, Science, ThomasFire, weather, wildfire. Bookmark the permalink.

17 Responses to Geology answers for Montecito and Santa Barbara

  1. Robert hazard says:

    It is really painful to see what a knowledgeable person such as Dr Keller has to say about the dynamics of the Montecito watershed. Clearly if he had been in the room with our ‘safety officials’ when the decision was made to use Hwy 192 as the demarcation line between mandatory evacuation and voluntary evacuation that line would have not stopped at 192. One would hope that experts like Dr. Keller would be called on to help draw a new flood risk map depicting mandatory evacuation zones but to do that the County would be admitting that the map they relied on before the tragedy was seriously flawed. And of course that would put the County in legal jeopardy.

    • Doc Searls says:

      Agree, Robert.

      Alas, we learn many things the hard way.

      Somewhere there is a report on how the Painted Cave Fire was a catalyst that got multiple administrative entities to cooperate under one “incident command.” Maybe it was another fire. The point is the same: multiple specialties need to converge in order to prepare for and deal with disasters like this. I am sure there is a similar history, way back, that gave us the Los Angeles Flood Control District.

      Hmm… I just went there, and here is how the text on their index page starts: “The Los Angeles County Flood Control Act (ACT) was adopted by the State Legislature in 1915, after a disastrous regional flood took a heavy toll on lives and property. The Act established the Los Angeles County Flood Control District and empowered it to provide flood protection, water conservation, recreation and aesthetic enhancement within its boundaries.”

      Santa Barbara County has one of those too. But I am sure it is less preoccupied with debris flows than “Flood,” as the LA entity is called, because debris flows here are rare, while on the face of the San Gabriel Mountains they are frequent enough to be treated as a constant threat. That’s why the debris basins at the mouths of canyons there tend to be many acres in size. Or many square miles in some cases.

      In looking at the mountains above Montecito today, I couldn’t help but assume that it’s time for bigger basins. But bear this in mind: they won’t be pretty.* Or cheap.

      [Later… Thanks for pointing out the Sepulveda Basin Recreation Area in your comment here. Such a great example of how we know together more than any of us know alone. My friend and co-writer of several things, David Weinberger, has a great book on how this works called Too Big to Know: Rethinking Knowledge Now That the Facts Aren’t the Facts, Experts Are Everywhere, and the Smartest Person in the Room Is the Room. His point there is also why I tend to prefer writing about a subject like this one in a blog rather than in a newspaper or magazine. We can all improve our understanding together, and I don’t have to pose as an authority whose job is to deliver final-draft answers to everything.]

      On Twitter, @TCBoyle asked, “any conclusions drawn? Other than that all this is destined to repeat and repeat?” I replied, “I think it depends on what our scientists find in their hikes up the canyons. If the stream beds are now bare of rubble re-landscaped over Montecito or carried off to landfills and beaches, we’ve got another couple hundred years. If not, we build LA-scale catch basins.” But that’s just a best guess. I look forward to what Ed and his colleagues find out. And hope in the meantime we get enough rain to fight the next drought while not washing more mountain down over Montecito.

      • Robert hazard says:

        There is quite a difference between the topography of the La Basin and Montecito. In Montecito the mountains and the ocean are far closer leaving very little room for catch basins of a size that could contain the massive amounts of debris that came cascading down on that Tuesday morning. Also from the LA catch basins to the ocean most if not all the creeks are concrete lined now. As are in fact quite a few of the creeks in Goleta. Turning the bucolic creeks of Montecito into concrete lined channels would certainly reduce flooding but not likely to be accepted by the community. In truth there are probably no good options for Montecito. The die was cast by decades of developments on a flood plain and on the banks of creeks. In my opinion the best that can be hoped for is a restructuring of the agencies that developed and implemented the terribly flawed evacuation plan.

        • Doc Searls says:


          On the matter of catch basins, some are already there. And I suspect there might be room for larger ones back up in the canyons. I suspect they might make make for ugly hiking, but not spoil the views up from below. Or not much, anyway.

          I doubt anyone would recommend concrete creek beds. (Though I was looking at a concrete one in Montecito today. It was Oak Creek, running from the culvert under Brooktree to the culvert under E. Mountain Drive. It was bare, because a small debris flow filled the upstream side of the culvert, pushing more debris, including what appeared to be somebody’s front gate, across the street. Some also flowed down toward the concrete stream bed, covering a pair of stairways, but that was the extent of the mess—unless it was bigger and already cleaned up.)

          L.A.’s whole situation is different—with the exception of the need to deal with debris flows coming out of the mountain front. The San Gabriels are less foliated, higher, steeper and produce many more debris flows than we tend to see here. That said, we do have them. And the situation isn’t much different for Santa Barbara, Summerland, Carpinteria, Ojai and Goleta. Had a giant rain fallen on the mountain front above Santa Barbara right after the Jesusita fire, what followed would likely have been very similar. And you’re right about agency reform.

  2. Mac Bakewell says:

    Wonderful stuff, Doc. Thank you for doing this.

    One quick correction:

    > Where the flow widened when it hit the Montecito Creek culvert under Olive Mill Road,

    There is no point at which Montecito Creek runs under Olive Mill Road, so that “culvert” would actually be the bridge under Hot Springs Road just north of the Olive Mill intersection.

    Montecito Creek bridge on Hot Springs Road
    34°25’50.2″N 119°38’28.8”W
    Google Maps:

    Annotated Topo Map

  3. cj says:

    Clicked on the “terrific animation” and downloaded only to find I can’t open anything. Is it possible to post this in another form?

    • Doc Searls says:

      Unfortunately, cj, that UCSB site does not make it easy.

      You have to click on Download: Southern California Tectonics movie and related images (52 MB). This pulls down a file called Open that and you get a folder called dSoCalifTect. Inside that folder is are a bunch of files, all produced by Tanya Atwater, now of Scripps in San Diego, when she was still at UCSB, back in the early ’00s. The animation is the file called “” I tried to put it on my blog’s server, but it balked because the file is too big. Then I put it on my own server (at, and for some reason it wouldn’t play from there. No idea why.

      That’s why I wrote a narrative description of what it shows. I think I might now add another visual from that folder, which should also help.

  4. Doc Searls says:

    Thanks to that link, Robert, I just added an corrective addendum to my comment above.

  5. Mac Bakewell says:

    Re your map “augmented with labels for the canyons and creeks (with one exception: a parallel creek west of Toro Canyon Creek)”:

    I’ve puzzled over that one. Pored over lottsa maps, none of which named either the creek or the canyon. I even asked Ray Ford, and then finally stumbled on it myself. I still lack corroboration, but I think it’s simply called Toro Canyon West.

    Also not sure if it was Toro Canyon East or West that caused the damage (as shown on your source map) at 321 Toro Canyon Road. The two creeks run pretty close together at that point, then diverge with West draining into the ocean at Loon Point, and East , uh, farther east along Padaro Lane.

    Strange that after so many years here that it would take a disaster to motivate me to learn a few place names.

  6. Doc Searls says:

    Thanks, Mac, for your work on the case. I just updated the map in the post. Note that “West Toro” goes straight down to the ocean from the mountains, and that a branch creek (which I’ve left with a ?) is where some damage occurred as well.

    Where did you find that map, by the way?

    In my own diggings I found Santa Barbara County
    Flood Control and Water Conservation District
    Final Updated Debris Basin Maintenance
    and Removal Plan
    June 2017
    , which describes plans to remove debris basins, to restore natural settings and allow fish to pass upstream (presumably when the stream is actually wet). This includes the Cold Spring, San Ysidro and Romero Canyon basins. In fact all were scheduled for removal last fall, and were barely noticed by the debris flows of January 9.

    Please read it, folks. I’m only beginning to get my head around it.

  7. Ajf says:

    My inner rockhead thanks you. Very sorry for lives lost. Would like to give a shout out to the topic and practice of controlled burns (please see “changing our relationship with fire” in the latest issue of Bay Nature magazine) it’s worth discussing and exploring. Target stores is selling hoodie of with that well meaning but misguided fire suppressor Smokey the bear. He needs to update his slogans to focus on suburban fireproofing concepts and practices (see Steve Inskeep’ s report on 60 minutes from last July or august.)

    • Doc Searls says:

      Thanks, Ajf. I sometimes think my inner rockhead is outer too much of the time, since I look at the world largely through a geological lens. Glad that came in handy here.

      It’s interesting to me that our state tree, the redwood, is adapted to fire. And the state flower, the California Poppy, is adapted to earthquakes (because—as I understand—it likes lots of fresh minerals around exfoliating rocks in dry soil).

      I believe one reason there is less controlled burning in coastal California is that so much of it burns over anyway.

      • Robert N Hazard says:

        Actually back in the 1970’s as I recall the Los Padres Forest embarked on an ambitious plan to do controlled burns along the South Face of the Santa Ynez Mountains from Gaviota to Matilija. The plan was to create a dozen or so fuel breaks from Camino Ciello down ridges to the foothills creating blocks of fuel that would be individually burned in early winter months at a 10 year or so frequency. They went as far as doing an Environmental Assessment. Unfortunately it never materialized and I heard it was because of funding. I think the powers that be in Washington felt it was not the responsibility of the Feds to fund fire protection strategies designed to protect communities that allowed people to build homes in fire prone areas.

  8. Ajf says:

    Controlled burns are practiced in the major forests since around the late 1970s or early 1980s. We hiked through a few on the toulleme trail. It was also why we slowly saw less of Smokey the bear around that time.

    But yes I know the sequoias have not been able to reach the upper Sierra , relegated to middle and lower sierra, possibly due to insufficient fire.

    Also in Oakland hills we’ve been using large goat herds to clear non-native species. Imagine they could also be used to to clear forms of fire fuel and underbrush. They are available for hire, a set of 50 or so goats along with some border collie and their humans who move the goats in subsections from right to left across the hill over the coarse of abt 7 days. Assume this is practiced down in my former town Santa Barbra (Goleta side of the tracks.)

    Did not know that abt the poppy. Love this state.

  9. Ajf says:

    I’ll try to follow up to ask abt jurisdiction of Los Padres. We’re trying to release next year’s funding now in some areas up here for efforts just like you describe.

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