Grizzly bears and other large mammals were once common at Año Nuevo, and grizzlies in particular were a dominant factor in the animal life of this region. They were a constant threat to the Indians who lived here for centuries, and they were still a significant danger for Spanish and early American settlers during the 18th and 19th centuries. It was a grizzly, for example, that killed William Waddell in 1875, near the creek that bears his name at Big Basin State Park, just south of Ano Nuevo. And it was not until about the mid-1880s that the last grizzly in the Santa Cruz Mountains was killed.
Most of the animals that now live in the reserve are nocturnal. Bobcats, mountain lions, coyotes, foxes, raccoons, skunks, weasels, brush rabbits and black-tailed deer are all regular residents. Bats can also be seen after dark.
Reptiles are often found sunning themselves on warm days. Common western yellow-bellied racers and coast garter snakes eat small rodents and insects. One of the most colorful snakes in North America, the rare and endangered San Francisco garter snake, inhabits marshy areas and feeds on amphibians.