THE JURASSIC (170-150 MA) MEXICO-ALASKA MEGASHEAR, A CONTINENTAL-SCALE FAULT BETWEEN THE GULF OF MEXICO AND ALASKA
In Oregon, MAM steps east within the Blue Mountains where contraction suggests transpression. The Methow basin and the Relay Mountain Group of the Tyaughton basin in British Columbia probably lie NE of MAM. From southern Alaska and northwestward correlative transtensional basins include Gravina, Dezadeash-Nutzotin, Wrangell Mountains, Matanuska Valley (southern Talkeetna Mountains), Tuxedni (Cook Inlet) and southern Kahiltna basins.
Principal fault segments, inferred to correspond with the trace of MAM, include Mojave-Sonora megashear, Melones-Bear Mountain, Siskiyou and Soap Creek Ridge faults, Ross Lake fault zone, as well as Harrison Lake, Bridge River suture, Lillooet Lake and Owl Creek faults. In western British Columbia, MAM corresponds with the mega-lineament along the southwest edge of the Coast Range batholithic complex. The Kitkatla and Sumdum thrust faults, probably formed initially as Late Jurassic strike-slip faults as did the Denali fault and more northerly extensions including Talkeetna, and Chilchitna faults.