As it turned out, it was a controlled burn off, being actively patrolled by rangers. I drove down the dirt road next to the burn off and jumped out here and there to take photos (as one does).
This shot shows just how much smoke was about. The road follows the line of power line poles.
I only jumped out of the car for small periods of time since the smoke was very thick and tended to make my throat sore after a while.
View all photos taken: Wednesday, 4th April 2007, This photo: 1:38pm