It burned the past few days along the Salt River bottom near 91st Avenue and Southern.
The fire never threatened any structures, but investigators are still working to discover how it started.
The Bureau of Land Management officials say the river bottom is like a desert forest that has sprouted up, which is cool until the forest catches fire.
The River Fire roared across 10 acres of river bottom that is full of desert vegetation.
From the 7th Avenue bridge south of downtown Phoenix, you can see the mesquite, creosote, and other desert vegetation. The entire valley is enjoying a green winter following a wet monsoon.
"We had a lot of rain last summer, and we had a lot of rain in the fall, so yeah the vegetation is there, but it's soon going to start dying once the temperatures get hotter," said Brian Scholl with the Phoenix Fire Department.
The vegetation explosion isn't just along the river bottom; many valley neighborhoods that bump up against mountain preserve land are seeing green and loving it.
"It's just stunning, really stunning," said Darcy Hayne.
Darcy Hayne's condo in Phoenix has the mountain preserve off his back patio but says the management company keeps the brush from growing too close.
"So they try to keep this clear, so I'm sure at some point they clear all this out so there won't be a fire hazard," he said.
Phoenix Fire says next month as it heats up they are going to start checking to make sure that dried vegetation isn't causing a hazard.
"What we tell people is whenever you have dry vegetation around your house just get rid of it, keep your grass nice and mowed, and keep everything watered because it does die, get rid of it," said Scholl.