RENO, Nev. (AP) — Authorities in northern Nevada are asking for information from the public about how a large grass fire started.

The fire burning in the Pyramid and Grass Valley areas north of Sparks was initially reported late Friday and by midday Saturday had grown to 19.5 square miles (50.5 sq. kilometers), with no structures reported lost or threatened.

Federal, state and local agencies are investigating the cause of the fire and asking for information from anybody who saw a vehicle leaving the vicinity when the fire was reported shortly after 5 p.m.

The Pyramid Highway was closed for about six hours overnight at Sutcliffe.