The Pacific Northwest is a region in the northwest of North America. There are several partially overlapping definitions but the term Pacific Northwest that span the United States and Canada. The term Northwest Coast is often used when referring only to the coastal regions. The term Northwest Plateau has been used to describe the inland regions, although they are commonly referred to as "the Interior" (which in British Columbia is by convention capitalized and is used as a proper name). The inland portion of the U.S. is called the Inland Empire. The region's biggest metropolitan areas are Seattle, Washington, Vancouver, British Columbia, and Portland, Oregon. The region has an Oceanic climate ("marine west coast climate") in many coastal areas, typically between the ocean and high mountain ranges. Alpine climate dominates in the high mountains. Semi-arid and Arid climate is found east of the higher mountains, especially in rainshadow areas. The Harney Basin of Oregon is an example of arid climate in the Pacific Northwest. A Subarctic climate occurs farther north. The Pacific Northwest was occupied by a diverse array of Native American peoples for millennia, beginning with Paleoindians who explored and colonized the area roughly 15,000 years before Europeans arrived. The Pacific Coast is seen by a growing number of scholars as a major migration route for late Pleistocene peoples moving from northeast Asia into the Americas. Archaeological evidence for these earliest Native Americans is sketchy--in part because heavy glaciation, flooding, and post-glacial sea level rise have radically changed the landscape--but fluted Clovis-like points found in the region were probably left by Paleoindians at least 13,000 years ago. Even earlier evidence for human occupation dating back as much as 14,500 years ago is emerging from Paisley Caves in Central Oregon. European exploration began as early as 1579 with Francis Drake possibly landing along the coast, but exploration began in earnest in the 1700s. The first permanent non-Native settlement in the American portion came at Fort Astoria in 1811.