[4] Light-colored granite, about 50 to 70 million years old (Eocene Epoch to Cretaceous Period) has been sculpted by glaciers that gouged deep U-shaped troughs throughout the monument.

Across from the Salmon River and Portland Canal and the settlement of Hyder, Alaska, small glaciers occupy high areas of the northeast part of the monument.

Soule and Through Glaciers cover high plateaus and valleys in the Lincoln and Seward Mountains, where one peak rises to 6,250 feet (1,900 m) above sea level.

Western hemlock, Sitka spruce and western red cedar dominate the prolific rainforest vegetation; wildlife in abundance includes both grizzly and black bears, many species of salmon, whales, mountain goats, and Sitka black-tailed deer.

The region was first visited by Europeans in 1793 when George Vancouver explored up Behm Canal, the prominent sea-filled glacial trough along the western margin of the monument and separating it from Revillagigedo Island.