Palos Verdes' Moving Hillside, 70 Years After It Started Sliding

A hillside south of Los Angeles has been sliding for seventy years, and in 2024 the city reported it moving nine to twelve inches a week — fast for ground. The Portuguese Bend landslide began in 1956 when Los Angeles County extended Crenshaw Boulevard down the slope, placing road fill on an ancient dormant slide underlain by bentonite clay. That clay, when wet, turns slippery, and the slide's base rides on a sheared bentonite bed about thirty to forty feet down. After moving up to forty feet a year in the early 1980s, dewatering wells slowed it to about a foot annually, but something changed after 2022 and movement accelerated sharply. By 2024 the city drilled sixteen new wells, and by May 2026, after a wetter-than-average winter, movement had dropped to about one and a quarter inches a week. The ground hasn't stopped, but it slows when water is pumped off the clay, and holding it there means pumping every day.