Flying over the Rockies can be extremely turbulent at times. Used to commute fairly often from LHR to SFO via JFK and the usual flight I took from JFK to SFO was an American Airlines flight AA5? or similar. This was back in the late 70, early 80's. I always stayed strapped in as on more than one occasion I had seen trays/drinks passengers and flight attendants doing the zero G routine. Even heard the Captain [AA had an audio channel for aviation geeks] ask for a number of level changes and say at one point "I have been flying this route for years and I have never had so much turbulence." Because of nearby traffic also requesting level changes we often just had to grin and bear it.
It was seeing the amount of wing flex that kept my eyes wide open!