Historical Settlement of North America

The closest indigenous to settle to Los Angeles settled in current San Diego about 25 and 15 thousand years ago. Los Angeles was part of New Spain during 1650. Then in 1821 Los Angeles was part of Mexico. In 1848 there was the Treaty of Guadalupe Hidalgo which happened after the Mexican War. This is when Los Angeles became a part of the United States. Los Angeles was first considered a frontier outposts. Today the majority of new Americans are from Latin America and Asia.

Source: 

The Geography of North America, 2nd Edition

Hardwick, Shelley, Holtgrieve