Maybe you mean 1940s? The Bay Area benefited from fairly massive government subsidies to the Military Industrial Complex in California. WW II shifted military attention to the West Coast and San Francisco Bay was a major Naval Base. The Atomic Energy Commission took over and expanded Lawrence Berkeley Lab and established Livermore Lab. The aerospace industry moved to California due to the continuous availability of good flying weather and proximity to aluminum sources based on hydropower. This was mainly to southern CA, but a lot of aerospace electronics came from the Bay Area. NASA also established Ames Research Center. Plus, as its congressional delegation grew in size and influence, and during the Reagan years, Federal money continued to flow into the state.

In the 1850s there was the Gold Rush, which was unplanned. Around 1900 the southern CA oil boom made it the largest oil producing state in the US.

Look up the history of Stanford to see early investments in the infrastructure of the Bay area. I agree post-war was when the rapid expansion happened but many of the important foundations were laid using gold money and railroad money. Similarly Caltech in the South land shows work prior to world war II. La was already in aerospace powerhouse when world war II happened.

Thanks for pointing out the oil boom I left that out because I forgot