Gold is often found alongside quartz - as water erodes the quartz, the gold is carried away by the water.
Interesting links:
Post on dry washing for gold:
http://goldismoney.info/forums/showthread.php?t=415908
That poster's "Encyclopedia of Prospecting" http://nevada-outback-gems.com/prospect/chris_prospect.htm
Have always thought it would be neat, even if not profitable, to buy a pan and see if a few bits of gold dust can be found.