The Denali Fault system, a major crustal break in Alaska and northwestern Canada, is characterized by horizontal movement although vertical separation has been suggested for parts of the system. Essentially all of the dextral displacement on this structure apparently has occurred during the Tertiary and Quaternary. About 350 km of dextral displacement occurred between 55 and 38 Ma ago on the McKinley. Shakwak and Dalton segments and displacement there since 38 Ma ago cannot be more than about 40 km. Holocene displacement has taken place on the McKinley and Totschunda segments and the western part of the Shakwak segment; high microearthquake activity on the eastern part of the Shakwak and Dalton segments has been cited as evidence that this part of the Denali system currently also may be active.