Many are familiar with the Cascadia Subduction zone now in the news, where an ocean floor plate off the Pacific northwest coast is sliding under North America. As it does so, magma forms under the above Cascade mountain ranges with the result that volcanoes, like pimples, erupt from the chamber of magma below.
Those chambers of magma under the mountains are extensive and interconnected across an area of nearly a thousand miles from the Canadian Cascades down to Mt.Lasson in California.
For those who do not know, magma which never reaches topside in an eruption and is later found exposed by erosion, becomes granite (such as the batholith in Wyoming and much of the Sierra Nevada mountains in California.)
Add a little geothermal percolating, faulting and good luck and you’ll have the copper, gold, silver and other metal ore deposits of tomorrow (well several tomorrows down the road.