The Hilton Creek Fault lies along the eastern Sierra Nevada front near Mammoth Lakes in eastern California, marking part of the boundary of the Long Valley Caldera. It is a normal fault, dropping the caldera and valley floor down relative to the rising Sierra block along the Basin and Range margin.
Its position at the edge of a large, restless volcanic caldera makes it especially active, with earthquakes often clustered in swarms linked to both tectonic strain and underground magma movement. Fresh scarps trace its path across glacial and volcanic deposits.
The fault was involved in the intense 1980 Mammoth Lakes earthquake sequence, which included four magnitude ~6 shocks in a single week and prompted concern about renewed volcanic unrest at Long Valley. Its ongoing activity keeps it under close monitoring by geologists.