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YOUR OROGENOUS ZONES DEPT./
CANYON REJUVENATION DIV.

Princes come, princes go.
An hour of pomp and show, they know!
Princes come; and over the sands,
And over the sands of time, they go.
Wise men come,
Ever promising the riddle of life to know.
Wise men come; ah! but over the sands,
The silent sands of time, they go!
Lovers come, lovers go,
And all that there is to know,
Lovers know; only lovers know.
— Robert Wright and George Forrest, Kismet, 1955, commissioned and debuted by the Los Angeles Civic Light Opera.

Fifty years ago today, February 9, 1971, occurred the deadly and devastating San Fernando Earthquake, aka the Sylmar Quake. https://ktla.com/news/local-news/l-a-marks-50-years-since-deadly-6-6-magnitude-san-fernando-sylmar-quake/

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It was felt most in Sylmar, where it caused huge damage to the old Olive View Hospital. It put an end to the long era in which Los Angeles geologists wrote studies about finding oil wells; now they would all be about how to “predict the Big One.” (Lately, happy to report, they’re all about block rotation!)

The Sylmar shaker ushered in the modern idea of building according to seismic safety codes, CalTrans started to re-invent freeways, and the DWP and Army Corps. had to figure out what to do with all the eggshell-brittle dams and reservoirs up there, Hansen Dam and the Chatsworth Reservoir, and Lopez and Pacoima dams (the first three were drained, the last retro-fitted). The epicenter was just over the Pass, in Placerita Canyon, or rather, deep under the alluvial surface deposits of Placerita Canyon. Maybe some, or all of these landscapes were left as they are, for me to photograph, during the Sylmar Quake.

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The Los Angeles Basin of California derives its name, and the San Gabriel River and Mountains theirs, from the names first incanted upon them by Fr. Juan Crespi, Franciscan missionary and diarist of the Portola expedition. On July 28, 1769, when the Spanish explorers came up the coastal plain from San Diego, they camped on the mesa above the banks of the Santa Ana RIver. This was right at the edge of the Los Angeles (named later) Basin. There was an earthquake lasting ‘half a Hail Mary.’ At every encampment the expedition made that week, at each of the principal drainage rivers of the Eastern and Central Transverse Range Blocks — Santa Ana, San Gabriel de Los Temblores, and the Rio de Porciuncula de la Reina de Los Angeles, there were massive earthquakes. Then on the days after, while marching north, there were ominous aftershocks. On August 3, Lady Day, when the party reached Yangna, the Tongva village where LA was founded downtown, and while delicate negotiations were going on, there was such a big one that the tremendous noise and shaking equally terrified the Tongva, the Spaniards and their pack animals. These were not events the Indians or the Franciscans took lightly. As soon as the Spanish left the Valley, leaving the Basin, the earthquakes stopped.

The Portola earthquakes were all within the old Farallon Plate subduction zone, the corner of an active spreading center which hit like the point of an arrowhead at Los Angeles, slipped under the continent, where its sides, still spreading, were driven under the plate as far as Santa Ana, and here, at the top of the Valley. This may have given birth to the San Andreas Fault. Maybe these landscapes were left there, as they are, for me to photograph during that incredible historic week in LA history.

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I went behind Sugarloaf, 2,074 feet, to see what lies atop and behind and beneath, and why it looks like an old extinct undersea volcano pushed up to mountain height. Hint…

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The Pangean Riviera was a very old, very flat place, first formed 1.7 billion years ago. It had already, likely many times, grown up great crystalline mountains, that had then eroded down to flat plains of boulders with fabulous rocks tumbling lazily over a wide white sandy beach, drizzled with run-off from the creeks. But sea level fell; and the beach got cliffs which got full of oak terraces, which drained copious mud and soil and rocks onto the white sand. When sea level rose, the white sand would swirl under the surf in huge undersea dunes. Sea level fell again, and more oak terraces would form in the drainages, even higher than before. This was the Embayment of the San Fernando Valley. Then came the Eocene intrusions, and uplift.

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3 million years ago when a big chunk of Orange County broke off and was captured by the Pacific Plate, and was pushed obliquely up the coast, so that the “prow” of the broken-off fault block (the beach town of Valley Village) SLOWLY slammed straight into the Pointe of North America’s ancient coast (Sylmar). Patient reader, Sylmar shattered.

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At that point, the Riviera’s long flat plain of white sandy beach was littered by every size of boulder. Under faulting half of the crust got sucked and crunched down into a new subduction zone, deep enough to melt the sand and boulders and cause magma chambers to boil. Meanwhile, under the prow of the WTR block more layers of the beach sand and rocks were pushed up, up, up — and then each time let crash. They rose and slumped down, three or more cycles. Sea levels rising and falling too, in their own cycles. At some point the magma chambers underneath couldn’t take it anymore, and ruptured to the surface in great tubes, underwater, over the sandy lagoon floor, melting the new sand and rock into the old sand and rock, making new kinds of sandy rock.

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