Its hard for me to comprehend just how radically different the motherlode looked back in tertiary times. Most rivers ran north/south instead of east/west.
And they actively eroded rich quartz veins, producing placer deposits 200 ft thick in places. Now the modern rivers and creeks continue to cut into those old rivers, creating totally new rich gold deposits. If you ask the old-timer professional dredgers, most will say the best claims are downhill of the "ancient rivers
of gold". If you look on google e., you can spot a whole lot of gulches, creeks, and rivers actively cutting into those old rivers. Just look for gray, rusty areas
of somewhat open terrain - its likely to be part of the tertiary channels.