The McGarrs came from County Tyrone, Ireland.The name was McGarrah or something a bit longer that was hard to pronounce, thus all the shortened variations.Go to that "other" message board for a better explanation than I can give.
Some went to Canada, others landed in New York and took the same routes west as most of the rest of Americans.Quite a few wound up in California. Some stayed Catholic, some left the Catholic Church.
Also don't forget to look at GenForum McGarr, McGary, McGarry, etc.
What would help is if everyone would put up their line--just the names and birth and death dates.That would help all of us figure out this puzzle.