California infrastructure was originally scaled for around 20m people. There are currently currently around 40m people and rising living in the state.
There are huge cyclical environmental events - periods of drought, wildfires, torrential rain and flooding (the entire central valley flooded in 1892, killing 40k people, bankrupting the state and wiping out housing, cattle and crops).
We have a mediocre electric grid that fails if any of the above environmental events happen. We allow 95% of rain water to flow into the ocean then promote panic about global warming when the inadequate reservoirs are depleted in dry spells.
Attempts were made to verticalize housing in the 1970's bay area, with predictable results from building life cycles such as Geneva towers in San Francisco.
https://www.foundsf.org/index.php?title=Remembrance_of_Genev...
We don't need to pack people like sardines into metropolitan areas any more. We need to create smaller, more human living spaces closer to resources. There is so much undeveloped land in the state but we are wrecking historically important locations instead of thinking new development. The YIYBY activists are obsessed with existing cities, they are rooted in the past.