Mount Sanford older volcanic rocks (Pleistocene). Chiefly a sequence of interlayered thick lava flows, flow breccia, and debris and mudflow deposits that are mostly of andesitic of basaltic andesite composition; locally palagonitized. The few samples that were collected from unit are microporphyritic to porphyritic olivine basaltic andesite. * * * Flows and breccias are locally separated from overlying Sanford lava flows (Qsl) by slight angular unconformity. Source or sources unknown; maximum thickness about 450 m, but base not exposed.
Geologic map of the Gulkana A-1 Quadrangle, south-central Alaska