I found out in 1978 when my husband and I were headed to Lake Powell on our honeymoon and stopped to visit my grandparents.
My grandmother in 1948 with my cousin Norman:

The air conditioner was rasping and gasping in the late summer evening, and I could barely hear my grandmother because she had taken out her teeth and was almost whispering:
"Neither of my grandfathers was very practical," she began.
I won't tell you the whole story, but she said her grandfather Heffernan fought in the civil war and then was involved in the Irish invasion of Canada. As a result he was 'requested' to leave upstate New York and go west to seek his fortune. I didn't hear any more about that invasion for many years, but have lately found quite a bit about it on the Internet:
"The Fenian raids of the Fenian Brotherhood based in the United States on British army forts, customs posts and other targets in Canada were fought in order to bring pressure on Britain to withdraw from Ireland, between 1866 and 1871. They divided many Catholic Irish-Canadians, many of whom were torn between loyalty to their new home and sympathy for the aims of the Fenians. The Protestant Irish were generally loyal to Britain and fought with the Orange Order against the Fenians.
While the U.S. authorities arrested the men and confiscated their arms afterwards, there is speculation that many in the US government had turned a blind eye to the preparations for the invasion, angered at actions that could be construed as British assistance to the Confederacy during the American Civil War. There were five Fenian raids of note:
Campobello Island Raid (1866)
Niagara Raid (Battles of Ridgeway and Fort Erie) (1866)
Pigeon Hill Raid (1866)
Mississquoi County Raid (1870)
Pembina Raid (1871)
Ironically, although they did not do much to advance the cause of Irish independence, the 1866 raids and the inept efforts of Canadian colonial troops to repulse them helped to galvanize support for the Confederation of Canada in 1867. Some historians have argued that the debacle tipped the final votes of reluctant Maritime provinces in favour of the collective security of nationhood, making Ridgeway the “battle that made Canada.â€
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I don't know which raid my great-great grandfather participated in, but will try to figure it out sometime, based on when he came west. He never really settled down to anything. His letters and papers show he looked for work as a mining engineer in the La Plata County gold mines, and he died on a ship headed to the gold fields in Nicaragua. My cousins have his last letter to his wife where he describes what he as been told about the gold to be found, and every time he wrote the word, he capitalized it: Gold, as some would capitalize the word God.