The Pacific Grove Monarch Sanctuary is merely one of approximately 400 overwintering sites along the California coast. However, due to the number of monarchs returning to the Sanctuary year after year, the Xerces Society for Invertebrate Conservation ranked it as the 6th most important California overwintering site in a 2016 report.
Pacific Grove's George Washington Park is also a part of the original overwintering habitat. However, urbanization, aging of the trees, and environmental stresses have caused a decline of this habitat. The City is attempting to reverse this decline with an aggressive campaign of tree planting, mulching, and trail improvement.
The proliferation of Australian eucalyptus trees, first introduced into this country in the 1850s, has also affected traditional overwintering patterns by providing a tree that is not only well-suited to sheltering monarch clusters, but also provides the butterflies with a convenient nectar source since it blooms in winter. Monarchs cluster in the eucalyptus trees at the Monarch Grove Sanctuary, as well as in eucalyptus groves at Natural Bridges State Park in Santa Cruz, and at the North Beach Campground in Pismo Beach near San Luis Obispo.