Are Region Names Capitalized?
Popular names of regions are capitalized:
Most popular names—such as the Sun Belt or the Fertile Crescent—cover large or ill-defined areas and could be considered singular, but occasionally a popular name will be plural. For example, the name Twin Cities refers to two specific cities (Minneapolis and St. Paul, Minnesota) and therefore is plural.
Silicon Valley is in California.
The Twin Cities are having great weather this week.
Get more tips like this in The Grammar Devotional: