That fire, east of Stockade Mountain in central Malheur County, has been named the Crowley Creek Fire.
A nearby fire that had been thought to be contained jumped fire lines Tuesday afternoon.
The U.S. Bureau of Land Management says the fires are burning in typical terrain for the region, in grass and sagebrush.
The BLM says more firefighters and equipment have been dispatched.
The agency also revised downward its size estimate for five small fires on state land in Harney County near the South Fork of the Malheur River. The BLM says those total about 250 acres. It said fire crews are holding the line there.
The lightning struck Monday.