DAWSON CITY, Yukon Territory - Modern-day prospector Shawn Ryan is hot on the trail of what he believes could be the monster lode source of the 6 million ounces of placer gold recovered from historic Bonanza Creek of Klondike Gold Rush fame.

For more than a century, geologists and prospectors have searched for the source rock that dumped a golden treasure into the creek and lured tens of thousa...