Dating from prehistoric times, the redwood forest ecosystem that Henry Cowell Park shares along with the other mountain parks such as Castle Rock, Portola, and Big Basin, reigned supreme over much of the northern hemisphere. Today these tallest trees on earth are only found along a 450 mile corridor stretching from southern Oregon to the southern limits of Monterey County in California. Even within this range, redwoods are restricted to the moist fog belt that blankets the stream canyons within 30 miles of the sea. Over time, redwoods have evolved to become fire resistant, thanks to their layer of thick fibrous bark. Covered with fire scars dating back hundreds of years, some of the oldest and largest of the trees in the park's main redwood grove approach 300 feet in height and are perhaps as much as 1500 years old.

Climate
Although the park is located nearly at sea level, it reaches an elevation of over 800 feet, which allows for the formation of chaparral communities on the high, exposed ridge-tops. Known as "elfin forests", these shrubs have adapted to the hot dry environment and seldom grow more than 3-8 feet tall.

Vegetation
California bay, tan oak, big leaf maple and Douglas fir are the redwoods' companion trees. Assorted ferns, redwood sorrel and wild trillium provide the ground cover. Between the redwoods of the stream canyons and the chaparral of the ridge tops lie the mixed evergreen forests. Live oaks, madrones, and an occasional buckeye are this community's broadleaf trees. Knobcone pines, Douglas firs and Ponderosa pines are the cone bearers. The Ponderosa pine is the most unusual tree species in the park, as they normally only grow in the Sierra Nevadas above 3,000 feet. It is quite extraordinary to see them at such a low elevation, and so close to the sea.