Graded bedding is usually explained as the result of a large amount of mixed sediment being discharged into quiet water. Examples would be a flash flood carrying a pulse of sediment into a lake, or an underwater landslide on the continental slope pouring onto the deep sea floor, or a tsunami washing over a beach into a lagoon. The coarsest clasts fall to the bottom first, followed by smaller and smaller particles until the water is clear.
Graded bedding signifies an energetic environment of some sort, but other features must be found to get a more precise idea of that environment. This particular locality, in the Orinda Formation west of Orinda, California, is thought to indicate a freshwater lake in a fault basin near vigorously uplifted bedrock hills to the west. Those hills have since been carried far to the north along the San Andreas fault system. The pulse of sediment that created this bed may well have been triggered by an earthquake.
Inverse grading, in which large particles lie above small ones, is occasionally found. Its exact cause is a standing problem in sedimentology.
