The Hatcher Pass schist consists mainly of metamorphosed and deformed sedimentary rocks, of Late Cretaceous to Paleocene age.

[9] West of Government Peak, the Arkose Ridge Formation lies to the south of the schist and the contact is a low-angle detachment fault.

Locally, quartz diorite or gneiss bodies occur on the arkose-schist contact west of Government Peak.

[10][11] On Government Peak, a 90 Ma (million years old) rock unit variously mapped as gneiss, or as intricately intermixed amphibolite and quartz diorite, or as a migmatite, and most recently as a mafic unit of gabbro and pyroxenite with local foliation and mylonitic textures structurally underlies the Arkose Ridge Formation and outcrops in between the Hatcher Pass schist and the arkose.

East of Government Peak and the Little Susitna River the mafic rock unit is in contact with the Arkose Ridge Formation to the south and the felsic plutons to the north.