Wind-blown power line, dragging chain, bad wheel bearing, bad exhaust system on a vehicle (catalytic convertor innards, for example), somebody parked in tall enough grass, fool with a welder, lots of other reasons that I've seen or heard of.
We had seven grass/forest fires near the ranch, last year, the two largest we got stopped at 3200 and 3600 acres.
One was a powerline fire and on two of them we found exhaust system parts. Traced it to a particular pickup (not mine) and I paid to have it repaired - didn't need a repeat! I'm hoping for none this year.
