Having walked on it, it really doesn't feel any hotter than the sidewalks. And in the morning and evening (only time it really makes sense to go walking there most of the year) it's significantly nicer than the asphalt.

This is something that I fail to understand - why are there so many people there? Is there unobtainium in the hills that can only be mined from the region? Prior to modern air conditioning, why would people setup there when there are seemingly more hospitable areas?

People did prefer living in colder areas before AC.

The arrival of AC meant there was suddenly a lot of very cheap land around cities that are extremely unpleasant without AC. This resulted in migration and a housing boom which drives up the economy attracting more people.

Sure enough, Wikipedia says the population in 1940 was only 65k (which is still too many, but whatever). I would still assume that AC installation was very uneven and a luxury at the time.

I would guess that swamp coolers were fairly common.

Yeah, and those actually work in the desert unlike in coastal areas

[delayed]

Large silver and turquoise mines, basically.

Cheap land

The only person I know that lived near there had fibromyalgia, and had deliberately moved there from NY as they felt better in that climate. So YMMV I guess. They didn't actually live in phoenix, don't know how much difference that made.

Can confirm the heat. In the early 1990s I got bumped from a flight out of Phoenix because it was so hot the density altitude meant they couldn't load the plane as heavily as usual.