There is a desert in California.
California . California also has the nation 's most populous county , Los Angeles County , and its largest county by area , San Bernardino County . The Central Valley is a large , flat valley that dominates the geographical center of the U.S. state of California . San Bernardino County , officially the County of San Bernardino , is a county located in the southern portion of the U.S. state of California . Located in southeast California , the thinly populated deserts and mountains of this vast county stretch from where the bulk of the county population resides in two Census County Divisions , some 1,422,745 people as of the 2010 Census , covering the 450 square miles ( 1,166 km2 ) south of the San Bernardino Mountains in San Bernardino Valley , to the Nevada border and the Colorado River .