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
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.