Based on the part of the country you were in, maybe air being lifted by the terrain disrupted relatively smooth airflow your plane was flying through? Because you were starting a descent, your aircraft was leaving the altitude(s) affected by the lifted/disturbed airflow. Maybe the event felt worse than it actually was. I was non revving the other night and we hit probably the worst turbulence I have experienced in a medium to heavy pax jet--the pax were vocal and drinks were flying....but at worst we didn't pitch or roll more than a few degrees. It probably *felt* like we did though!