Tens of thousands of monarch butterflies congregate along the California coast to winter each year, and it is a spectacular sight. From mid October through the end of January, they take shelter in eucalyptus groves. Two prime spots for local viewing: Natural Bridges State Beach in Santa Cruz and Pacific Grove Monarch Grove Sanctuary near Monterey.
Tip: make sure you go on a sunny day, or the butterflies won't be flying!
http://www.parks.ca.gov/?page_id=541
http://www.ci.pg.ca.us/monarchs/default.htm
