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It's hard to get a sense of it from the pictures, isn't it.

I lived in the Santa Cruz mountains, which had the last big landslide with many fatalities. Here is a write up of that tragedy:

Jan 5, 1982: Landslides kill 33 in California Previous DayJanuary 5CalendarNext Day
0 On this day in 1982, (January 5) a series of landslides near San Francisco, California, kills up to 33 people and closes the Golden Gate Bridge. In all, an amazing 18,000 different landslides took place in the San Francisco Bay Area following a very heavy rain storm.
Two fast-moving fronts carrying extremely heavy rain passed through San Francisco in a 36-hour period beginning on January 4, during which the area received an amount of rain equal to half its average annual precipitation. Some areas received as much as 24 inches of rain on January 4 and 5. On January 5, the rain began to trigger thousands of separate landslides in the Bay Area hills.
Almost without exception, the slides caught their victims completely unaware. San Francisco State University professor Kai-yu Hsu was in the basement of his home in Tiburon. Suddenly, there was a deafening roar and, within seconds, the home was gone--it crashed into a park at the bottom of a hill. His son, Roland, witnessed the tragedy while standing just outside the home.
In all, about 7,800 homes and businesses were seriously damaged by slides and falling trees. Roads became impassable when mud and large boulders crashed down onto them. The Golden Gate Bridge even had to close due to a landslide. When seven homes in Love Creek collapsed on a hillside, 10 people died instantly. It is believed that between 22 and 33 people were killed in total. Damages exceeded $100 million, and the region was declared a federal disaster area. It was the Bay Area's worst natural disaster since a 1906 earthquake.
Using aerial surveillance in the days following the storm, officials determined that about 18,000 separate slides occurred. In most areas, homes have since been rebuilt on the original lots, using sub-surface pipes and retaining walls to help prevent a repeat disaster.

I believe a fresh logging road was partially responsible for the collapse. The Santa Cruz mountains were always full of landslides and collapsing stuff. Roads would disappear all the time.