Green’s Dictionary of Slang

a native of New Hampshire, known for its granite quarries.

1845		St Louis (MO) Reveille 14 May 2/4: The inhabitants of [...] New Hampshire [are called] Granite Boys [DA].
1866		Amer. Citizen (Butler, PA) 26 Sept. 2/4: Nicknames [...] New Hampshire, granite boys.
1871		Semi-Wkly Louisianan 31 Aug. 1/3: The Nicknames of the States [...] Nebraska, bug eaters; Nevada, sage hens; New Hampshire, granite boys; New Jersey, blues or clam catchers.
1885		North Amer. Rev. Nov. 433: Among the rank and file, both armies, it was very general to speak of the different States they came from by their slang names. Those from [...] New Hampshire, Granite Boys.
1909		J. Ware Passing Eng. of the Victorian Era 146/2: Granite-boys (American). People of New Hampshire, which is a granite-producing territory.