As both uplift and erosion continued, the Stanislaus River gradually carved the rugged canyons it flows through today, and contributed to the vast alluvial deposits that make up the flat floor of the Central Valley. Some of these fluvial sediments, originating from gold-bearing veins in the granite batholith, were deposited as placer gold in the river bed to be discovered later during the California Gold Rush. The lower course of the river is geologically young, dating to no earlier than the Holocene; the river has continually cut new channels through its sediments and filled in older ones, creating a sequence of river terraces.