The megafan consists of sediments eroded from the rapidly uplifting Himalaya.
As a relative lowland, it had been a site of deposition for sediments eroded from surrounding mountain regions.
During the ensuing Pennsylvanian epoch the same sediments eroded from the mountains had formed an expansive coastal plain.
The sea was gradually filled in by sediments eroded away from areas of higher elevation in the western region of the state.
The basin later became filled with sediment eroded from the Rockies.
Over time, these basins would have received large volumes of sediment eroded from Tharsis and the southern highlands.
During the Late Devonian the state's seas had begun filling in with sediments eroded from mountains outside of the state.
These sedimentary rocks originated as sediment eroded from the Ancestral Rocky Mountains.
Excavated sequences of remains of paving show that sediment eroded from the surrounding hills was already raising the level in early Republican times.
In areas near shore some of the signal may also be due to sediments eroded from beaches as well as from sediment laden river plumes.