Since it began, the rim fire has burned more than a quarter million acres in and around the National Park making it the largest wildfire own record in the sierra nevada. And that reminded us of another fire 17 years ago in that same area. It was called the ackerson fire and it burned nearly 60,000 acres and had a devastating effect in that area for months to come. Heres ktvus john fowler as the ackerson fire burned. Drew to a close as twilight descended on the sierra. This helicopter one of four spent the day in the river valley. It is steep, inaccessible and dangerous and the site of just one of the sierra forest fires now raging out of control. Extremely difficult for ground crews. The battle here has been from the air. These helicopters that we have here and these air tankers are whats keeping these helicopters in shape. Reporter into a forest that hasn t burned in a century. It now flames up intensely. We have heavily logs, older brush, older trees that kind of thing. Burns hotter.