Surrounded by urban development, Milagra Ridge forms what biologists call an island ecosystem. Here, wildlife is isolated from other habitats, feeding and migration corridors are compromised and exotic species can easily invade native habitat. Despite this isolation, Milagra Ridge hosts a surprising number of threatened and endangered species including Mission blue and San Bruno elfin butterflies and the California red-legged frog. Milagra’s proximity to urban development, its limited size and its rare wildlife make it exceptionally sensitive to human disturbance. Therefore, visitors are required to stay on trails and pets must be leashed. More from NPS here.