Alaska is not:
  1) an island off the coast of Southern California
  2) an island in the Gulf of Mexico
as US weather maps often indicate.
Alaska is:
  1) Part of North America i.e. on the same continent as the 'lower 48'
  2) One of the 50 states of the United States of America
Anchorage is located in Southcentral Alaska (in the approximate position of the red dot)

Map of North America

The North American continent extends:
   north to the Arctic Ocean and
   south to the Caribbean Sea and the isthmus of Panama.  
Major islands of North America include:
  in the north: Greenland, Newfoundland and the Arctic islands of northern Canada
  in the south, the tropical islands of the Caribbean.