NEO GEO : Turn! Turn! Turn!

On days when the wind or rain’s tiny fingers carry away the red and brown gauze that blankets the Los Angeles Basin, it’s always a shock to sit in morning traffic and see the gorgeous San Gabriel and Santa Monica mountains towering over the north end of the city. So ragged. So improbably large.

But most improbable of all is that these mountains have been spinning around like toy tops and ballerinas for millions of years.

“The San Gabriel block has rotated clockwise about 53 degrees and then back-rotated about 16 degrees,” marvels UC Santa Barbara geology professor Bruce Luyendyk, who made the discovery. “It’s pretty astonishing.” Although other scientists, skeptical when Luyendyk first raised his theory in the ‘70s, have since come around,most Angelenos have no idea of our mountains’ migrations.

The almost unimaginably large force that has caused the mountains to spin like a clock’s hands is the northward movement of the vast Pacific Plate in relation to North America. Twenty million years ago, the mountains that now range east to west north of Los Angeles lay more than 100 miles to the southeast. They rotated into their present position by way of what Luyendyk calls “subducted slab capture”: A chunk of ocean floor that had been diving beneath the North American Plate became fused to the northwest-drifting Pacific Plate, affecting the crust and mountains riding above as if a cookie sheet were gradually slid out from under a loaf of French bread. Hold one end of the loaf (the mountains) down with a finger and the other will swing around as you pull on the sheet.

The rotation of the mountains also created, in effect, our home: When the ranges swung north, the crust behind them was stretched open and created, over millions of years, the Los Angeles Basin.