Los Angeles is not a desert- it’s a Mediterranean climate. It has a wide variety of soil types, both well draining and expansive soils that absorb absorb compacted soils that don’t absorb water.

It used to have many wetlands that absorbed water and sediment. A few areas are left in west LA but the development of the city over the wetlands with poor drainage plans is the issue. Instead of making a network of areas that drain water and create green space engineers decided to just push all the water into one giant channel.