Type the title of the map and underline or italicize the title.
Type the descriptive label using the word "Map."
Type the city of publication followed by a colon, then the publisher and the date of the map's publication if it is available. Date format is the day followed by the month then the year, with no commas.
Write the title of the online collection and underline or italicize it.
Provide the date the map was posted or most recently updated.
Type the name of the project or database reference (if applicable), underlined or in italics.
Type the name of the sponsoring institution, which in this case would be the United States Geological Survey.
Provide the date you accessed the USGS website and type the website page information. The citation should look like this:
"Map of 1860 Colonial America. (in italics or underlined) Map. St. Louis: Smith, 1860. Colonial American Map Collections. (in italics or underlined) 11 May 2010. Maps and Legends. (In italics or underlined) United States Geological Survey. 15 June 2011 http://earthquake.usgs.gov/earthquakes/shakemap/nc/shake/71596420/."