Final answer:
The early twentieth century population growth of California was driven by the Gold Rush, World War II economic opportunities leading to urban migration and jobs in defense industries, as well as significant migration from Mexico due to political and economic factors.
Step-by-step explanation:
The early twentieth century population growth of California was a result of various factors, including immigration, urbanization, and economic opportunities. The discovery of gold in 1849 lead to an influx of people from around the world, creating a diverse polyglot population in boomtowns like San Francisco. This Gold Rush substantially increased the state's population from a few thousand to about 100,000 almost overnight. Additionally, with the onset of World War II, there was a swell in migration to California's urban centers to fill jobs in defense plants and shipyards. This economic need also brought about the bracero program, encouraging the migration of thousands of Mexican agricultural workers.
Furthermore, political and economic turmoil in Mexico during the 1910s led to a significant number of Mexican immigrants settling in California. This, along with the steady increase in farm production, urban development, and inflow of European immigrants, substantially contributed to California's early twentieth century growth spurt. By the 1930s, immigrants from Mexico made up 12 percent of California's population, with nearly a million people migrating from Mexico to the U.S.