Every time we get what we call a gully-washer (boulders the size of cars tumbling down the river), we know that residual gold hung up on the canyon sides will get washed into the main channels to replenish gold, so I can't see why it won't work in California as well.
glacial moraine containing pretty much unsorted material,gold just slyghtly waterworn due to glacial transport
false bedrock is a smooth clay layer
river running nearby .
In this conditions even small floods that carry away morainic material replenish finegold and medium to big floods bring also new bigger gold .It,s just easyer for the gold to travel on a smooth claylayer i guess ,no cracks to get trapped in and there,s much less force required to wash out the gold from morainic deposits.
So it depends on the circumstances how easily new gold washes in to your waterway.
cheers