Those structures are - or were - earthquake shacks, also known as earthquake cottages or refugee cottages. With the help of the Army, the city built the shacks in the wake of the 1906 earthquake, which left 225,000 San Franciscans without homes. They placed the tiny, one-room cottages in city parks, and residents whose homes had been destroyed paid $2 a month to live in them. At one point, more than 16,000 people lived in the shacks - approximately three for every 250-square-foot dwelling.