The Kelly Girl 1-4 claims straddle the axis of the American Creek anticline: an open, slightly inclined regional fold of Unuk River, Hazelton assemblage, and Betty Creek, Bowser assemblage, volcanic, volcaniclastic and sedimentary rocks. The property is almost entirely underlain by Lower Jurassic, red and green volcanic conglomerates and sandstones of the Unuk River Formation. Middle Jurassic volcanic conglomerates, breccias, and crystal and lithic tuffs of the Betty Creek Formation unconformably overlie the Unuk River rocks along the west boundary of the property. A series of normal faults are aligned with the axial plane of the American Creek anticline. A major splay of these faults occurs near the north edge of the property from which a cross-cutting fault trends to the east.