Los Angeles wasn't anything in 1850 when California became a state. Like it's been said, tons and tons of settlers stayed in the Sacramento area after making the long crossing from the east coast to the west coast. Also, the Gold Rush played an enormous role in the population boom of northern California. During this time, the population of southern California was in the low thousands.
Los Angeles was just a massive fruit orchard up until and including the 1920s. The Indians had missions in the area and that was about it. However, with the introduction of the Hollywood movie industry, the bringing of water by Mullholland, the worlds first freeway in the late 40s (the 110 freeway), and many other factors... the area exploded from 2,000 people in 1900 to 14,000,000 people in 2004 in Los Angeles County.
My posts/replies are strictly my opinion and not that of any company, organization, or Southwest Airlines.