The park contains almost all of the Waddell Creek watershed, which was formed by the seismic uplift of its rim, and the erosion of its center by the many streams in its bowl-shaped depression.

It is part of the Northern California coastal forests ecoregion and is home to the largest continuous stand of ancient coast redwoods south of San Francisco.

Some of these trails link Big Basin to Castle Rock State Park and the eastern reaches of the Santa Cruz range.

[3] The park has many waterfalls, a wide variety of environments (from lush canyon bottoms to sparse chaparral-covered slopes), many species of mammals (deer, raccoons, an occasional bobcat) and abundant bird life – including Steller's jays, egrets, herons and acorn woodpeckers.

Numerous resources would have been available to California Indians in the old growth forests, such as basketry material, plant foods like acorns and bulbs as well as animal prey for hunters and perhaps traditional sacred places.

[4] In October 1769, the Portola expedition encountered the redwoods of southern Santa Cruz County, and camped at the mouth of Waddell Creek, in present-day Big Basin, later that month.

Their movement to preserve the Big Basin redwood forest began at Stanford University on May 1, Soon after Santa Cruzans led an excursion to the park where seven men and two women formed the Sempervirens Club.

The Big Basin Inn offered cabins to rent, a restaurant, general store, barber shop, gas station and photographic studio.

[citation needed] Save the Redwoods League purchased a 564-acre (228 ha) parcel known as Cascade Creek in 2020 that links Big Basin with Año Nuevo State Park.

[6] The CZU Lightning Complex fires started on August 16, 2020 and burned 86,509 acres across Santa Cruz and San Mateo counties.

[16] The burnt wreckage of 1,490 structures and 15,000 charred trees, mainly Douglas fir, had fallen or were in danger of falling onto the hiking trails.

[citation needed] Upon climbing to higher elevations, one will find the forest growing thinner, as redwoods are replaced by more drought-tolerant species.

[citation needed] Near the mouth of Waddell Creek is the Theodore J. Hoover Natural Preserve, a rare relatively undisturbed freshwater marsh.

[citation needed] Mammals such as black-tailed deer, western gray squirrels, chipmunks and raccoons are common, but foxes, coyotes, bobcats, and opossums are also present.

[citation needed] Many reptiles are also present, but aside from the ubiquitous Coast Range subspecies of the western fence lizard (Sceloporus occidentalis bocourtii), most are rarely seen due to their shy behavior.

[citation needed] Big Basin can be approached from the east, through redwood forest and coastal mountains, or from the coast, along State Route 1.

[18][20] Big Basin plays the part of the fictional "Bolderoc National Park" in the 1942 George Marshall film, The Forest Rangers.