Trione-Annadel State Park, State park in Sonoma County, California.

Trione-Annadel State Park covers 5,092 acres at the northern edge of Sonoma Valley, beside Spring Lake Regional Park in Santa Rosa. Its volcanic terrain rises from about 360 to 1,887 feet at Bennett Mountain, with oak woodland, chaparral, grassland, marsh and Douglas fir on cooler north-facing slopes. Ledson Marsh drains into Yulupa Creek, and streams such as Yulupa and Spring Creek run dry in summer.

The park was established in 1971 to protect the natural landscape. The area beneath its current boundaries was once home to the Wymore Quarry, which extracted stone for San Francisco's streets and buildings from the late 1800s until the 1920s.

The name comes from Annie Hutchinson, whose family owned land here around 1900; the spot was called "Annie's Dell". Author Jack London settled nearby in the same Sonoma Mountains in the early 1900s and drew on them in his writing. Visitors today pass cobblestone quarry sites and obsidian-bearing volcanic outcrops.

The park provides roughly 40 kilometers of trails suitable for hiking, mountain biking, and horseback riding at various difficulty levels. Plan visits during cooler months since much of the terrain is exposed with limited shade from trees.

The park's volcanic soil, Goulding cobbly clay loam, holds about 25 percent cobblestones, a remnant of the Sonoma Mountains' igneous past. Quarrying that stone boomed after the 1906 San Francisco earthquake, when cobblestones were needed to rebuild the city's streets. Joe Coney later mined perlite here, an obsidian product used in insulation, until the late 1960s.