Technically and geologically speaking, the mountains of Yosemite are formed much like an onion (and an ogre), with layers. The mountains are still moving and occasionally a piece of a layer slides off, sometimes with dramatic effect. Not too many years ago a piece about the size of three football fields slid off, possibly hit supersonic speed on the way down, and flattened a large area of the valley floor. Now there is concern about Curry Village since some "onion" activity has been occurring above that area.
To see scenery like Yosemite I will take my chances!
So to answer the question... YES!! If a tree falls in the woods and there is nobody around to see it fall, it DID happen. How do we know this? 100 years later it's still there!
Terminal Tower In Cleveland reflected in window across street last winter...and since glass is technically liquid and this tower is "terminal"could be this will let go any second just like Yosemite, guess the world is fraught with danger( bobq's slide account reminded me of the alaskan tsumani caused by a similar slide that denuded mountains way up the sides, so guess those things happen more than we think.)
Looking more like the initial drop of a roller coaster than a railroad, Saluda Grade is the steepest mainline railroad grade in the U.S. The photo might be better with a train in it but since it was such an operational nightmare Norfolk Southern has not run trains on Saluda Grade in over 8 years.