[JimSEA]

They are sedimentary rock. It is particularly prone to failure due to high clay content which when in contact with water has a tendency to be very slippery and rock failure is frequent. Clays are slippery in soil as well. A good article on landslides. I know it's specifically about Arizona but the information is valid elsewhere

[editor-surveyor]

.
Are you deliberately trying to change the subject?

Under current theory as it is articulated, the deep SOIL landslides that we frequently have are impossible if the Earth is older than 10-15K years old.

Of course it is doubletalk, but that is what gets called “scientific.”

.