The most commonly seen mammal at the Reserve is undoubtedly the desert cottontail (not to be confused with the brush rabbit). They can be seen around the visitor center, darting across the trails, or lying in the shade in the coastal sage scrub. Visitors who hike to the rivermouth via the 5th and Iris St. trail should keep an eye out for Black-tailed Jackrabbits, which are much lankier and larger than their cousins.
In general, mammals are much harder to spot than reptiles and birds due to their nocturnal (active during the night) or crepuscular (active during dawn and dusk) nature. Other mammal sightings within the Reserve include Long-tailed Weasels, California Ground Squirrels, California Voles, Deer Mice, Coyotes, and even Gray Foxes. Striped Skunks, Opossums, and a few species of bats are known to be around at night.