Like any developed economy, LA benefits from having many overlapping industries that seem to create a multiplicative effect in wealth generation. The total is greater than the sum of the parts.
It turns out if you vacuumed up the loose soil, rocks, people, buildings, fossil fuels, and cars from around the LA area, a four mile hole would remain.
My geography of the American West has always been fuzzy. When speculating about a potential trip West, I wondered aloud if it was possible to do Yellowstone in the morning, have lunch, and hit Arches National Park in the afternoon.