All of the large Classic Lillooet sites appear to have been abandoned about 1,100 years BP. It has been suggested that this was most likely due to a major landslide on the Fraser River that may have blocked salmon runs for years or decades and thereby destroyed the subsistence and trade economy of the remarkable Lillooet communities. There is a stratigraphic section near Lillooet which supports this theory.
Storage pits dated to 1,280 BP were dug into the overbank silts in the bottom of the section. Normally, these deposits would occur at the surface of the deposit. However, here, there is a level of river cobbles and boulders that occur above the overbank deposits, indicating that the river subsequently rose again. Overbank deposits again cover the cobbles and boulders as is normal in river deposits. These storage pits are now about 50 - 100 feet above the river level.
This stratigraphic section near Lillooet indicates that there was a major impoundment of the Fraser River about 1,100 years ago.