Thornewood Open Space Preserve, Regional park in San Mateo County, California.

Thornewood Open Space Preserve is a protected natural area in the Santa Cruz Mountains featuring Douglas fir and coast redwood forests alongside oak woodlands. The land is crossed by maintained hiking paths that wind through different forest types and connect to scenic spots within the property.

Julian and Edna Bloss Thorne developed the land in the 1920s, building a house designed by Gardner Daily and surrounding it with gardens that included Schilling Lake. When Edna died in June 1970, she left the land to the Sierra Club Foundation on condition that the 86-acre summer-home grounds remain undeveloped. The foundation donated the acreage to the Midpeninsula Regional Open Space District in September 1978, and in 1986 Robert Procter and his wife added 3.4 acres.

The name Thornewood comes from Julian and Edna Bloss Thorne, who developed the land in the 1920s and built a house designed by Gardner Daily, surrounded by gardens that included Schilling Lake. The lake was named after the neighbouring August Schilling land; both estates lay within Rancho Cañada de Raymundo.

The preserve has two main walking routes: one path winds through forested sections while the other leads to a natural water feature. Both trails are well-marked and suit visitors of varying fitness levels, though sturdy footwear and attention to trail conditions are recommended.

Schilling Lake, the preserve's pond, is named after the neighbouring August Schilling land, not after the Thorne family who created it. The lake is a protected wildlife habitat, and the Schilling Lake Trail gives brief views of southern San Francisco Bay, Palo Alto and Stanford University's Hoover Tower.