A jury has found an Eastern Oregon rancher and his son guilty of setting fires on federal rangeland.

The verdicts against Dwight Lincoln Hammond Jr., and his son, Steven Dwight Hammond, came Thursday in U.S. District Court in Pendleton.

They face a five-year mandatory prison term and fines up to $250,000.

The two were convicted in a 2001 fire set near Steens Mountain. Steven Hammond was also convicted in a 2006 fire near the Malheur National Wildlife Refuge. They were acquitted on charges from two other 2006 fires.

The prosecution argued that the U.S. Bureau of Land Management warned the Hammonds in 1999 against setting range fires to improve the grass for cattle, but they went ahead anyway.

The defense argued that lightning sparked most of the fires.