The granitic basement rocks at Kehoe Beach consist of a mix of granodiorite with inclusions of older metamorphic rock that are cut by light-colored dikes of aplite and alaskite. Aplite is a light-colored, fine-grained rock with granitic texture, consisting essentially of quartz and orthoclase. Alaskite is also a light-colored granitic rock that has orthoclase, microcline, and subordinate quartz. Both rock types lack mafic constituents.