“There's one on the ground there. Are there two? No way! Are they mating?” I turn to ask longtime monarch sanctuary volunteer, Barb Thomas. We hover over the two butterflies at our feet and discover that they are indeed attempting to mate. Surrounded by trees, we stand in the middle of the Monarch Grove Sanctuary, in Pacific Grove, California. California has more than 450 monarch sanctuaries, and this is one of the oldest known ones, located about a two-hour drive south of San Francisco. Monarchs overwinter in the sanctuary from about October to March.