Unlike the Mexican sites whose main threats are logging and conversion to marginal crop land, the sites in California are threatened by the large sums of money to be made by coastal land development. Also, natural aging and death of the trees in many groves is leaving breaks in the canopy, gaps that make the canopies unsuitable for butterflies in the winter. The situation in California is further confounded because most of the Monarchs overwinter in non-native Australian Eucalyptus trees, the removal of which is a major target of restoration along the coast.

In the United States, most of the Californian winter roosting sites are not protected, although several are located within state, county, or town parks. Some Californian coastal counties have enacted ordinances to protect winter roost trees, and the California state government allocated $2 million for acquisition of Monarch winter habitat. Outside of the overwintering sites, however, neither Monarchs nor their habitat and primary hostplant, milkweed, are protected. To the contrary, milkweed is often targeted with herbicide as a weed.