I lived in the Seattle area for 45 years and have ridden my bicycle through the area covered by that slide. I moved to Central KY in 2011. We own two fingers of a plateau about 80 feet over the valley below. My wife was asking about slides here. I’ve worked the dirt in both areas. here, if you dig down a few feet you get clay and limestone. It’s basically a big rock under us. Completely different.
It would have to be. We get torrential rains here on a regular basis (anything that can slide, has slid). That’s why I spent all day Saturday with my tractor re-grading the steep hill of our driveway that brings you up from the valley. It’s made of the dirt and when leaves clogged my ditch, it re-directed those torrential rain fed waters right down the middle of my driveway, creating an 18” deep and 12” wide grand canyon meandering right down the middle of it.
But when I dug out my ditch, I eventually hit the clay. It’s not going anywhere in a hurry.
The graded bank tends to assume it’s angle of repose.
A couple of dump truck loads of chert rocks would likely diminish that problem......................