The natural habitats of D. ensatus are damp temperate forests and clear, cold freshwater streams, ponds, and lakes.

The head, back, and sides of the salamander have a marbled or reticulate pattern of dark blotches on a light brown or brassy-colored background.

[7] California giant salamanders are preyed upon by the American water shrew (Sorex palustris) and the western aquatic garter snake (Thamnophis couchi).

Eggs are concealed several feet below the surface in cold, slowly flowing water often beneath rocks and coarse woody debris in stream bottoms.

[4][9] There is an unconfirmed sight record from Big Sur in Monterey County, approximately 75 miles (100 km) to the south of the documented population in the Santa Cruz area.

[4] Some California giant salamander larvae continue to grow into adults and become sexually mature without losing their external gills.

Adult-sized neotenes have a uniform brown coloring on their heads, sides, and backs and retained external gills which allow them to live in perennial streams as aquatic adults.