From Wood and Kienle (1990) 
: "Fourpeaked Mountain consists of small isolated volcanic exposures surrounded by the Fourpeaked Glacier. The exposures are found along ridge crests and cliff faces on the sides of ridges that radiate out from the ice-covered summit. Lava flows are interlayered with volcanic agglomerate in the isolated exposures.
"Orientation of lava flows suggests the present summit of Fourpeaked is probably the vent for Fourpeaked volcano. Extensive hydrothermal alteration of rocks in this area is consistent with this vent location.
"Fourpeaked is known only from limited reconnaissance studies. The lavas are porphyritic andesite."