One of the most distinguishing and memorable characteristics of the Santa Clarita Woodlands is the presence of bigcone Douglas-fir trees. Found at a relatively low elevation, this plant community (classified broadly as part of a mixed hardwood forest) is more ideally suited to the climatic regime of 18,000 years ago (wetter, cooler) than that of today (drier, warmer). This population represents a relic vegetation type that survives in the higher canyons on steep, shaded, north-facing slopes. Such vegetation is best represented in the headwaters of East and Rice Canyons.

Other elements of this mixed hardwood forest are canyon and coast live oak, California bay laurel, flowering ash, California black walnut, and bigleaf maple. Shrubs and herbs commonly found among these trees are toyon, poison oak, gooseberry, hollyleaf redberry, mountain mahogany, hairyleaf ceanothus, Mexican elderberry, creeping snowberry, coastal wood-fern, goldenrod, heart-leafed penstemon, bush monkey flower, miner's lettuce, maidenhair fern, elegant Clarkia, and Chinese houses. An extensive valley oak tree population occurs along the crest of the Santa Susana range, thriving on cloud and fog drip and approximately 21.8 inches of rain per year.

Many of the forests in the Woodlands have been burned by wildfires Where severe fire has created openings in the forest canopy, shrubs, flowering ash and California black walnut prosper.