The Nicasio region is a hydrologic zone containing the four main drainages of Nicasio Creek up to the ridgelines defining their basin. It includes the south fork of
Nicasio Creek extending from Moon Hill, along the ridge separating Nicasio from
San Geronimo and
Samuel P. Taylor State Park, and extending northwest towards the northern end of Platform Bridge Road; the east fork (
Lucas Valley fork) of Nicasio Creek extending from Loma Alta and the ridge on the north side of
Sir Francis Drake Boulevard, extending up through Big Rock and up towards
Big Rock Ridge; the Halleck Creek drainage, up to the ridges separating Nicasio from
Novato; the northern drainages extending along the ridgelines of Rocky Ridge, Hicks Mountain and Black Mountain. A major landmark in the area is the man-made
Nicasio Reservoir. Nicasio is surrounded by forested and open ridge lines surrounding a wide rolling valley. The area along Lucas Valley Road follows a narrow valley with mostly forested hillsides above it. Oak, bay, and fir trees are common in the area, and along some of the creeks stands of redwoods are still found. Wildlife is abundant; the Nicasio chickadee, a subspecies of the
chestnut-backed chickadee, was named by Robert Ridgway. Three main roads cross the area: Lucas Valley Road, Nicasio Valley Road, and the Point Reyes-Petaluma Road. Important pieces of public land in the surrounding area include
Point Reyes National Seashore, portions of the
Golden Gate National Recreation Area, and
Samuel P. Taylor State Park. ==Demographics==