The West Coast or Pacific Coast is the coastline along which the contiguous Western United States meets the North Pacific Ocean. As a region, this term most often refers to the coastal states of California, Oregon and Washington. More specifically, it refers to an area defined on the east by the Cascade Range, Sierra Nevada and Mojave Desert, and on the west by the Pacific Ocean. The U.S. Census groups the five states of California, Oregon, Washington, Alaska, and Hawaii together as the Pacific States division. 

As of the 2010 Census, the estimated population of the Census Bureau's Pacific Region was approximately 47.8 million (56.9 million if Nevada and Arizona are included) – about 15.3% (18.2% with Nevada and Arizona) of US population. The largest city on the west coast of the United States is Los Angeles. 

Major cities and metropolitan areas on the West Coast include (from north to south): 

However, of these aforementioned cities and metropolitan areas, only Los Angeles/Long Beach, San Francisco and San Diego are directly on the open Pacific Ocean. 

The history of the West Coast begins with the arrival of the earliest known humans of the Americas, Paleo-Indians, crossing the Bering Strait from Eurasia into North America over a land bridge, Beringia, that existed between 45,000 BCE and 12,000 BCE (47,000–14,000 years ago). Small isolated groups of hunter-gatherers migrated alongside herds of large herbivores far into Alaska. Between 16,500 BCE and 13,500 BCE (18,500–15,500 years ago), ice-free corridors developed along the Pacific coast and valleys of North America and possibly by sea.
When did it exist?
between 45,000 BCE and 12,000 BCE