Brush, often dense, grows on lower mountain slopes, yielding to open tundra as elevation increase. Glaciers occupy the headwaters of major drainages. Some nearby peaks are over tall. Geology The Willow Creek mining district lies at the southwestern edge of a great mass of granitic intrusions that form much of the Talkeetna Mountains. The area is within the Wrangellia composite terrane At Hatcher Pass a pervasively altered zoned 74 Ma (million years old) quartz diorite to tonalite pluton underlies the headwaters of Willow Creek and Fishhook Creek; most of the gold deposits occur in these rocks. A 67 Ma quartz monzonite pluton lies west and north of the older quartz diorite, a Cretaceous (?) quartz diorite pluton lies to the east. A high angle east-west fault passing through Hatcher Pass separates the plutonic rocks on the north side of the fault from the Hatcher Pass schist south of the fault. The Hatcher Pass schist consists mainly of metamorphosed and deformed sedimentary rocks, of Late Cretaceous to Paleocene age. The schist may represent subducted Valdez Group that was exhumed in the forearc region from beneath the Peninsular terrane. Both deformed and undeformed small felsic dikes occur in the schist. Several bodies of serpentinite are contained within the schist. West of Government Peak, the Arkose Ridge Formation lies to the south of the schist, the contact is a low-angle detachment fault. The Arkose Ridge Formation is unmetamorphosed but tilted and slightly folded, and consists of Tertiary (Late Paleocene to middle Eocene) sedimentary arkose, shale, sandstone, and conglomerate rocks that are clearly derived from the schists and intrusive rocks to the north. Locally, quartz diorite or gneiss bodies occur on the arkose-schist contact west of Government Peak. Minor basalt flows occur within the Arkose Ridge Formation. On Government Peak a 90 mya 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; south-dipping low angle detachment faults separate the units. 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. Gold-bearing (+/- Ag, W, Sb, As, Cu, Mo, Pb, Te,