Subject Index - Geography
Use U.S. Postal Service abbreviations (such as CO for Colorado and DC for District of Columbia) for states in bibliographies, references, and full addresses (those that include streets or post office boxes).
Denver, CO 80101
Don't capitalize words that describe general areas of the country or areas of a state.
northern New Mexico
Capitalize directional words when they designate specific or widely known regions; if in doubt, use lowercase.
the Midwestern states
the South Side of Chicago
Do not use parentheses around area codes in phone numbers. Parentheses previously were used to set off the three-digit code in a phone number because it wasn't always necessary when dialing the number. However, they are required in most instances now.
Use hyphens to separate the digits in phone numbers.
In text, consistently spell out states' names rather than using U.S. Postal Service abbreviations.
Colorado (rather than CO)
Wyoming (rather than WY)
You may use D.C. for the District of Columbia in text, in both formal and informal publications. When you include addresses or state names in full addresses (containing streets and cities), contact lists, reference lists, and bibliographies, however, you may use the following abbreviations:
Do not abbreviate the names of countries (including the United States) when they are used as nouns. Use "U.S." as the adjective form.
U.S. DOE program