The defense industry in southern California used to be huge until the 1980s. Lots and lots of ex-defense industry people moved to other industries. Oil and gas has gone through huge economic cycles of massive investment and massive cut-backs.

After the year 2000. dot com burst.

An tech employee posted he looked for job for 6 months, found none and has joined a fast food shop flipping burgers.

That turned tech workers switching to "flipping burgers" into a meme.

.com implosion, tech jobs of all kinds went from "we'll hire anyone who knows how to use a mouse" to the tech jobs section of the classifieds was omitted entirely for 20 months. There have been other bumps in the road since then but that was a real eye-opener.