According to the California Geological Survey Santa Cruz County is among the highest-risk counties for landslides in Northern California. "Santa Cruz stands out even within the Bay Area because it has higher mountains, steeper slopes, and it has weaker rocks," said Chris Wills, a state supervising engineering geologist.
The rock type composing the Nelson road landslide is Santa Cruz Mudstone. According to James Tait, "The silica cement which binds the Mudstone is fairly strong, making it fairly hard for a sedimentary rock. On the other hand, the formation is highly fractured and crisscrossed by numerous small faults." When combined with a steep slope, a road cut and rain, a "perfect storm" is created in which a landslide can occur.
The Nelson Road landslide is about 250 feet long and about 150 feet wide. It wiped out a power line and cut off vehicular access to 28 homes. The rocks came within 30 yards of some homes and continued to creep for some time after the primary slippage. A temporary bypass was built through a nearby neighborhood, making all but two homes accessible by vehicle.
After the March storms, Santa Cruz County declared a local disaster and Gov. Jerry Brown echoed the declaration. However, no disaster funding was attached to the state declaration. As of August 2011 no funding had materialized to repair an estimated $2.6 million in damage to the two-lane road, but as of 2016 repairs have taken place - see Update below.
You can see a video of the landslide here
Update
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