Description: From Hildreth and others (2003): "On its southwest side, the summit dacite rests on a coherent andesitic lava flow (61.7 weight percent SiO2) that yields a K-Ar age of 73+/-12 ka. The northwest ridge of the edifice consists mostly of a glaciated stack of thinner lava flows and breccias, but low on steep northern spurs of the ridge are two massive andesitic lavas (60 weight percent SiO2), each 100 to 200 m thick, which are probably glacially truncated coulees but, alternatively, might be older domes."
"An andesitic lava flow that directly underlies the summit dome of Trident I, about 100 m southwest of peak 6115, yields an age of 73+/-12 ka. Most of the edifice appears to lie stratigraphically beneath this lava, except for the mafic pyroclastic assemblage (unit tca, fig. 3 [in original text]), which apparently drapes many of the andesites and yields a 40Ar/39Ar age of 58+/-15 ka (Hildreth and others, 2003). Because much of the Trident I pile is banked against its eastern neighbor (dated at 143+/-8 ka), the active lifetime of Trident I appears to be reasonably well bracketed."