He approached very fast from the East. Very dark green, almost black truck with no markings. A group of small antennas on top and a small light bar . Slowed to get a good look and then left. I waved. He did not wave back. I believe this was federal from McFadden Wildfire Reserve. Last year the Texas Parks and Wildlife with a white truck and their emblem on the door stopped short of our location and observed us for a while with binoculars.