Huntington Beach's Central Park is one of several overwintering locations for Monarch butterflies, and as such, this can be a great place to spend some time in a large city park setting while the monarchs flutter throughout the air and tree branches around you.
Late each year, as the monarchs migrate back toward warmer climes, many return to traditional overwintering groves along the California coast, where they'll stay until the following spring when they head back for northern locales. Typically the monarchs can be seen from around October until late February or into March. Central Park is one of the areas in Orange County that significant numbers of butterflies have been spotted at, specifically at a grove of eucalyptus trees near the park's wooden amphitheater.
Your best chance to see the monarchs is to head to the wooden amphitheater located about a quarter mile northeast of the library building on a sunny afternoon. Have a seat on the top row of amphitheater seating, and relax. Given enough time and the right conditions, you'll soon notice the fluttering of butterflies along with spots of orange set on the eucalyptus leaves. The monarchs wait for warmer conditions to come to life, so check the sunny areas in the groves and the grassy areas, and ideally wait for the warmer mid-day hours to see the most.
The nearest parkng to the grove is directly east of the library's front entrance. From here it is a short walk along asphalt paths to reach the eucalyptus groves and amphitheater.