Against the mountains

Life on the front

Whew, my time in southern California really flew by. Now that I'm leaving, I'd like to tell you about the neighborhood I’ve been staying in, where my friends Jon and Bella live.

When I first I turned onto their street, back toward the end of post #3, there was a serious vibe change: after miles fully exposed to the rain on wide, flat, densely populated streets, suddenly I was on a one-lane road winding up into a lush canyon, enveloped by trees that muted the rain. A topographic map confirms that their street, Pasadena Glen, snakes directly up a steep-walled canyon into the foothills of the San Gabriel mountains. The neighborhood is contiguous with the Angeles National Forest, which contains the massive peaks that loom over Los Angeles, including the 10,000 footer, Mt. Baldy.

The morning after I arrived, the sky was clearing but everything else was still soaked. We walked out their front door and past towering cacti, coast live oaks, and fully-loaded citrus trees — pomelo, orange, kumquat, lemon. In five minutes we arrived at a small horse ranch, home to three racehorses enjoying a sweet retirement in the hills overlooking the city.

A very friendly retired racehorse.

There is a lot of wildlife in the neighborhood: deer, lizards, mountain lions, all sorts of birds. We walked past a tree that had been gouged by bear paws. It was incredibly serene, and more than a little wild.

Evidence of bears.

It is a strikingly peaceful neighborhood. Until it isn't. Shortly after I arrived, Jon handed me a book called “The Control of Nature”, by John McPhee, along with a warning that, since it had been raining for weeks, it might make for scary reading. I appreciated the reference, and the content warning was appropriate: the third chapter of McPhee’s book chronicles Los Angeles' battle against “debris flows”, the violent masses of boulders and liquefied rubble that, under certain circumstances involving lots of rain, burst forth from the mountains in canyons just like the one Pasadena Glen is built into. These debris flows sweep up anything in their path — cars, trees, entire houses.

And once you start to look, the defenses that have been deployed against debris flows are everywhere. The gunite-reinforced channels. The culverts dipping back and forth beneath the road. The massive fence of 1-foot-diameter brown columns, meant to filter out large boulders that might block the culverts. And, most impressively, the debris basin, with its 30-foot “perforated riser,” which allows water to drain out even if the basin were to fill up with boulders.

This fence was massive.

The debris basin below Pasadena Glen. More than 100 of these basins have been built along the mountain front.

Closeup of the perforated riser.

John McPhee is one of my favorite observers of the natural world, and reading his writing while in the exact place he was describing was next-level cool, even if the subject was a little spooky. McPhee likens the sequence of events leading to a debris flow to the charging of an eighteenth-century muzzle loader: “the ramrod, the powder, the wadding, the shot. Nothing much would happen in the absence of any one component.” As he explains, the debris flow risk comes from a combination of three factors: 1) steep, rapidly eroding mountains; 2) vegetation that is prone to intense wildfires; and 3) infrequent but extremely intense rainfall.

Here’s McPhee describing the vertiginous mountains:

The San Gabriel mountains are as rugged as any terrain in America, and their extraordinary proximity to the city, the abruptness of the transition from the one milieu to the other, cannot be exaggerated. The slopes average sixty-five to seventy percent. In some places, they are vertical... In such terrain, there is not much to hold the loose material except the plants that grow there.

And here’s what he has to say about the vegetation, known as chaparral:

...all chaparral has in common an always developing, relentlessly intensifying, vital necessity to burst into flame. In a sense, chaparral consumes fire no less than fire consumes chaparral. Fire nourishes and rejuvenates the plants.

In other words, fire is part of the cycle of life in these ecosystems. (Human fire suppression and global warming have made recent fires more intense.) The inevitable fires are the first step in the sequence of events leading to a debris flow:

After a burn, so much dry ravel and other debris becomes piled up and ready to go that to live under one of those canyons is (as many have said) to look up the barrel of a gun.

With everything in place, what ultimately sets off the debris flow is an extreme rain event, like the sequence of “atmospheric rivers” that were dumping on California earlier in January, back when I was in the Bay Area. Or, to take a historical example:

In January of 1969, during a nine-day series of storms, twelve inches of rain fell in one night. A debris flow hit [Andrew Ingersoll’s] cabin, broke through a wall, and delivered three feet of mud, innumerable rocks, and one oak to the Ingersolls. The family regarded this as "just a lot of fun," he said.

Hold up, Andrew Ingersoll? Andy is a preeminent planetary scientist and a professor at Caltech. I have read many of his papers. As I learned more about the debris flows and how destructive they can be, I had naturally started to wonder what types of people would choose to live there. Turns out, it’s a mix of professors and people who don’t know better (at least, that’s how John McPhee tells it). Here McPhee is conversing with Leon Silver, a Caltech geologist who used to live way up in a canyon:

JM: "Why does anybody live there?"

LS: "They're not well informed. Most folks don't know the story of the fire-flood sequence. When it happens in the next canyon, they say, 'Thank God it didn't happen here.'"

JM: "Why would a geologist live there?"

LS: "It's a calculated risk. The higher you build, the cooler it is. There are great views. And at night, up there, the cool air off the mountains flows down and pushes the dirty air masses back. The head of our seismological laboratory lives on the mountain front. In fact, most of the Caltech geology department lives on the mountain front."

As well-informed as my friends are now, they admit that they didn’t quite know what they were getting in to when they bought their house. (Of course, realtors don’t exactly lead with the debris flow risk.) But if they ultimately decide to stay long-term, they are in good company:

To the question “Why, then, do people live there?” the answer seems to be that they are like [the naturalist] John Burroughs: they would rather defy nature than live without it.

If you want to read the whole McPhee story (which I recommend), it was originally published in a two-part New Yorker article called "Los Angeles Against the Mountains." (The first part is available to read for free on their website, but the second is behind a paywall. You can always get the book!)

That’s all for now. Oh, and by the way: I’m on the train to Tucson!

—Jake

P.S. I am so grateful to Jon, Bella, and Sulu for hosting me during my time in SoCal. It can get lonely on the road, but not with these guys around. Especially not with Sulu around.