For anyone who doesn’t want to click the reddit link or if it dies in the future:

Death Valley is a quintuple whammy of rainshadows and being below sea level. You can think of as being a pot with those high mountains as the sides, and 282(?) Feet below sea level. Deep fuckin pot. Now think of the sky as a sheet. You can soak it with water and run it over the pot. As the sheet hits the edge of the pot it squeezes the sheet and all the water falls outside the pot. That’s what the mountains around Death Valley do.

That sheer dryness means the sunlight goes through with very little stopping it, then when it’s absorbed by the soil and rocks and radiates into the air, it’s not really carried out of the valley since it’s this dense mass of sub-sea-level air.