Well, I've worked in three continents, but have never (ever) travelled to the US, let alone been to Gilroy (which, as a matter of fact, I had never even heard of, until I read your post).
However, garlic farms sound simply wonderful, as does a garlic festival.
This time of year, wild garlic puts in an appearance, as the green leaves can be consumed; they are quite wonderful, (when very young) in salads, but can be steamed - or sautéed - exactly as one would prepare spinach, or chard, as the plant matures and the flavour intensifies and becomes a lot stronger before the bulbs of young garlic (also delicious, when young) first appear.