Paleontology and geologyIn the Early Tertiary, subduction continued to consume oceanic crust and bring magma close to the surface in the southwest. This process uplifted the southwestern part of the territory and formed the large blocks of granite that make up the Coast Range. Soon, however, subduction ended, and the continental and oceanic plates began to slide past each other. This motion continued to generate substantial volcanism and uplift in many areas, but it also created large faults in the territory. Volcanoes spewed out lava and ash over Yukon, and more lava reached the surface as the crust thinned and broke up along the faults. Eventually, valleys developed on the faults as they filled with sediment eroding from the mountains. Deposits of sandstone, siltstone, conglomerate, and coal accumulated in the valleys. Some of these deposits preserve fossils of wood, pollen, and cones from the pine, spruce, and other plants that lived here. In one area, part of the forest must have flooded, which killed the trees and left their fossilized stumps where they grew. |