National Park Service spokeswoman Alexandra Picavet said the blaze is intended to char about 30 acres in the Golden Gate National Recreation's Gerbode Valley to help eradicate the invasive plant fescue.
In the meantime, motorists on U.S. Highway 101 and residents of Sausalito are wondering about all the smoke in the air.
A Sausalito police dispatcher said she has received "about 100,000" calls from people wondering what is burning.
She said police have been told the burn will end around 4 p.m.
