Imagine for a moment that the mountains you see around the San Fernando Valley are taller—much taller. Actually, those mountains were much taller, but millions of years of torrential rains and flooding washed silt, sand, and gravel down their slopes to the bottom of the mountains. Over millennia, this erosion gradually raised the Valley's floor with alluvium while lowering the height of the area’s mountains. In this sense, rain is a great equalizer.

The geology of Woodland Hills can be placed in three classifications (Geological Survey of California, n.d.):

• Upper Miocene marine, found in the foothills of the Santa Monica Mountains
• Alluvium, found on the floor of the San Fernando Valley
• Upper Pliocene marine, found on the northern half of Chalk Hill north of the Ventura Freeway

Figure 1. Geology of Woodland Hills

The following sections provide information about geologic events such as earthquakes, landslides, and flooding that affect Woodland Hills. This information is intended to demonstrate the high probability of major earthquake occurring in the area. There are ways to mitigate this risk:

• Inspecting previous seismic improvements for thoroughness and quality before purchase of a property.
• Seismic retrofitting a building’s foundation to meet best earthquake-retrofit practices.
• Avoiding purchasing stilt-houses on steep hillsides or properties with foundation and/or drainage problems.
• Purchasing high-quality earthquake insurance as rated by A.M. Best.