Male California sea lions reach about 2 to 2.5 m (6.5–8 ft.) and 200 to 400 kg (440–880 lbs.). At maturity male California sea lions are much larger than females.
Female California sea lions reach about 1.5 to 2 m (5–6.5 ft.) and 50 to 110 kg (110–240 lbs.).
A California sea lion has a fusiform body shape that is sleek and streamlined.
California sea lion coat colors vary. Generally, adult males are chocolate brown, females and young males are tan, and pups are dark chocolate brown. As adult males age, the hair around their heads lightens to a light tan.
Most California sea lions appear dark brown to black when wet.
A California sea lion's foreflippers are large and winglike.
The foreflippers have all the major skeletal elements of the forelimbs of land mammals, but they are modified for swimming. The "arm" bones are shortened, and the flippers are lengthened by cartilaginous extensions at the tips of the finger bones.
The first digit is larger than the others. It's strengthened by fibrous tissue along the leading edge.
There are no claws or hair on the foreflippers.
California sea lions use their foreflippers in an up-and-down, wing-like motion to propel themselves through the water.
Like land mammals, sea lions have five digits in the hind limbs. They are lengthened by cartilaginous extensions.
Nails are visible on the middle three digits.
On land, a sea lion can rotate its hind flippers underneath the pelvic girdle, enabling it to support its weight and walk on all fours.
In the water, a sea lion extends its hind flippers and uses them to help steer.
A California sea lion has a small, flattened tail between the hind flippers.
A sea lion's coat consists of guard hairs with shorter fine underhairs. Each guard hair is associated with several underhairs. A thin film of oil secreted by glands under the skin waterproofs the coat.
California sea lions molt (shed their hair) once each year, gradually shedding and replacing most of the guard hairs and underhairs. This molt usually occurs after the breeding season.
- Immature and nonbreeding females molt in August and September.
- Lactating females and subadult males molt in September and October.
- Adult males molt from November to February.
On land, California sea lions groom their coats. One common grooming behavior is a doglike scratching using the nails of one of the hind flippers. They also rub against rocks or other sea lions or rub their hair with their foreflippers.