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The ice mass that covered the coastal mountains along the Pacific Ocean coast of North America from northern Washington state into southern Alaska. At its maximum extent, about 20,000 years ago, it connected with the Laurentide ice sheet to the east and with the Pacific Ocean to the west, and reached a thickness of some 3 kilometers (1 mile). The Cordilleran Geosyncline is a linear trough in the Earth's crust in which rocks of Late Precambrian to Mesozoic age (roughly 600 million to 66 million years ago) were deposited along the western coast of North America, from southern Alaska through western Canada and the United States, probably to western Mexico. The eastern boundary of the geosyncline extends from southeastern Alaska along the eastern edge of the Northern Cordillera and Northern Rocky Mountains of Canada and Montana, along the eastern edge of the Great Basin of Utah and Nevada, and into southeastern California and Mexico. The Old Cordilleran culture appeared in the Pacific Northwest about 9000 or 10,000 BC and persisted until about 5000 BC in some areas. Subsistence was based on hunting, fishing, and gathering. Simple willow-leaf-shaped, bipointed projectile points are characteristic artifacts.