In inhabited areas that are likely to experience a landslide, local and regional politicians, developers, and geologists have come together to reduce the damage caused by possible landslides. They take extensive measures to change the way water flows from mountain tops, bolt unstable rock material to sturdier underlying material, build retaining walls, and promote methods of retaining loose materials. The Genofiles' is McPhee's book experience what is known as a debris flow. Debris flows occur most commonly in stream valleys and resemble a texture similar to fresh concrete. They consist of water mixed with solid materials, most of which are a least as large as a sand particle, and can be as large as cars, and sometimes larger.
Debris flows can at times ooze along and at other times move as fast as the fastest river rapids.
The particular flow that McPhee described can be attributed to three of the triggers, previous earthquakes, heavy ran fall and human activities. The whole front of the San Gabriel Mountains had shattered and broken, by undercutting of streams, and local earthquakes. Their house build by a stream at the base of the San Gabriel Mountain range, filled up within six minutes, and at the end of the slide was buried under twelve feet of debris. Like many of their neighbors they did not feel threatened before the storm. They were confident in the man made concrete basins designed to catch the falling debris.