In 1939 the federal government purchased three houses on Sunnyside at East Blithedale. One house was demolished. The other two were moved to other sites. A post office was constructed on the property in the Spanish Mission revival architecture typical of a government building. It opened in 1940. In 1942, shortly after Pearl Harbor, an emergency receiving hospital was established in the basement. The reinforced concrete area below ground was thought to be a good place for safety in case of bombing. Ten beds were set up. It was expected that this casualty station would not be used unless regular hospitals were unavailable in an emergency. In 1982, a larger post office opened on Lomita Drive in the Alto Shopping area. The Sunnyside post office was sold to Smith & Hawken which remodeled it for offices. Since then, other companies have occupied the building.
Mill Valley had a bomb shelter. In 1942, an emergency receiving hospital with ten beds was established in the basement of the new post office on Sunnyside. The Alto post office replaced it 1982. Smith & Hawken bought the old one for office space.