Near Tucson, the birth of riparian forest

I remember well,  on our second trip to Tucson, making a day trip to the San Pedro Riparian National Conservation Area and walking out through a riparian forest there that was rich with mature cottonwoods, some willows and many other native plants that thrive with wet feet (roots). I jsut discovered this article which goes into some depth of how cottonwoods are thriving in a Tuscon-area watercourse.