A woman has died and her male companion has been severely injured following a cliff collapse at the Point Reyes National Seashore to the northwest of San Francisco on Saturday 21 March 2015. Nancy Blum, 58, described as a preschool teacher had reportedly been among a group of hikers that ventured onto a sandstone buff at Arch Rock, despite warning signs advising people to keep back following the opening of a fissure in the cliff face on Thursday 19 March. The hikers apparently believed they would be safe as long as they kept behind the fissure and were taken by surprise when the cliff collapsed from some distance behind it.
View of the cliff collapse at Arch Rock in the Point Reyes National Seashore on 21 March 2015. Sonoma County Sheriff's Office.
The sandstone cliffs of the Point Reyes National Seashore are considered highly unstable and prone to crumbling and collapses. They are easily undercut by the actions of waves at the cliff base, with the rocks above being brittle and prone to sudden collapses. The area is also close to the San Andreas Fault, which cuts directly through the National Seashore, and movement along this fault can further weaken these formations.
Geological Map of the Point Reyes National Seashore showing the approximate position of the 21 March 2015 cliff collapse. Modified from Geology at Point Reyes National Seashore and Vicinity, California: A Guide to San Andreas Fault Zone and the Point Reyes Peninsula, United States Geological Survey (2005).
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