Waterlogged

We decided to spend a few days in the warm lands of Mazatlan the other day and coming back last night we encountered a rather abrupt slowdown from 85 mph or so to 0.
And we were making such good time, no slowdowns in Guadalajara, so I though we would be home before the street lights came on, but nope.
Rocks, or should I say boulders the size of pick up trucks created a traffic stop for miles behind us.
We sat motionless for about a hour before the traffic started inching along. When we finally  got to the cause of what I though was a 3 or 4 car pile up, it was a few boulders the size of pick up trucks or small cars, lodged under a tractor trailer rig.
 It was luck that one of these massive stones didn't land on the cab of the tractor, one of the boulders lodged itself under the trailer moving into the passing lane, thereby only allowing a narrow passage of the backed up traffic to pass.

We got home about 9:30, it was real dark already.