California is mostly desert, national forest, and fire country. LA, and SD exist in their current state due to large scale water works that bring water from outside of California.

For an American comparison, the northeastern US is home to 43% more People than California and is only 17% larger. In both California and the US, the population is concentrated on the coasts.

Would it be so surprising that a nation with a large coast, mild weather, and plenty of water would have a large population?