High Quality Content by WIKIPEDIA articles! The term California Plein-Air Painting describes the large movement of 20th century California artists who worked out of doors (en plein air), directly from nature in California, United States. Their work became popular in the San Francisco Bay Area and Southern California in the first three decades after the turn of the 20th century. Considered to be a regional variation on American Impressionism, the painters of the California Plein-Air School are also described as California Impressionists, the terms are used interchangeably.