I've been dredging offshore Nome for 10 or 11 years, I'm one of the most successful ones out here, mining from 5 to 65 feet. The practical answer is that gold is where you find it.
The long answer, from reading the research of others is that a long time ago, magma formed a load deposit of gold in the mountains North of what is now Nome. The load deposit was eroded into placer by alluvial action and other forces of water, rain, rivers, glaciers, oceans. Most of the gold settled out in rivers and streams, which moved around quite a bit. During the second to last ice age, around 100k to 300k years ago, glacier action ground and carried the material out to the sea, which at several points in time was much higher and much lower than it is now. As the theory goes, where the glacier met the sea, it dropped out material, this is called a glacial thrust zone. There are several distinct "beaches" where glacial alluvial gravel with gold is found in significantly higher concentrations. The modern beach, 1st beach at about +15, 2nd beach, about +35 feet, and third beach about +50 feet (I may have these elevations off by several feet), these were all mined extensively 115 years ago. The richest was the highest elevation (the first gold to drop out), each beach getting weaker as it got farther from the load source (aka mother load).
In the ocean there are several defined "beaches", what they think were beaches. At -15ft, -30', -45', -60', and -80ft. The -80ft does not have any higher gold in it that background average. Background average in Norton Sound and Bering Straits is still higher than most areas, but not commercially viable to mine.
The gold bands also look sort of like a rainbow with one end near shore at Nome's Snake River and the other near shore at Jess Creek. There is a lot of ground out there that is not suitable to mine.
As others have pointed out, other actions after the glacial thrust have moved the gold around, rivers below current ocean levels, ice sheets, currents, aliens, all sorts of actions. Which brings me to the point where it doesn't do much good to know how the gold got there, the gold is where you find it.