Trione-Annadel State Park is a state park of California in the United States. It is situated at the northern edge of Sonoma Valley and is adjacent to Spring Lake Regional Park in Santa Rosa. It offers many recreational activities within its 5,092-acre (2,061 ha) property.

The rock formations of Trione-Annadel have played a central role in its history: its volcanic origins, the Native American use of obsidian, the early 1900s mining of cobblestones, and modern hikers' appreciation of its volcanic rock outcrops.

These lands were occupied by the Wappo and Pomo people in prehistoric times, who would have primarily inhabited the riparian zones and the marsh perimeter. Annadel includes what some biologists consider the best example of undisturbed northern oak woodlands in existence. Visitors can enjoy the park's diverse wildlife and scenery during any time of the year but are perhaps most rewarded from April through June when most wildflowers are in bloom.

The 2017 Nuns fire burned the southern portion of the park. In 2020, the Glass fire burned the northern edge of the park.

Plant communities include California oak woodland, riparian woodland, Douglas fir forest, chaparral, grassland, and marsh. The dominant plant community is the oak woodland, which has a canopy of coast live oak, Garry oak, black oak, Pacific madrone, bigleaf maple, and California laurel. Canyon live oak occurs in swales and creeks. In the oak woodlands, the dominant understory plants are native bunchgrasses, toyon, wild blackberry, coyote brush, and western poison-oak. The latter covers nearly one quarter of the understory in the park. Douglas fir occurs in some of the steeper, cooler riparian zones and on north-facing slopes.

Common animals in Annadel include black-tailed deer, western gray squirrel, raccoon, skunk, and opossum. Bobcat and mountain lion are occasionally observed. There are many bird species, including the California scrub jay, Steller's jay, acorn woodpecker, black phoebe, and dark-eyed junco. In moist areas, amphibians such as the rough-skinned newt can be found.

The southern reaches of Annadel are drained by Yulupa Creek and other tributaries of Sonoma Creek, while the northern flanks are part of the Santa Rosa Creek watershed. Eastern slopes are drained by Yulupa and Sonoma Creeks, while the western slopes are part of the Spring Creek watershed. Many of Annadel's streams are dry in the summer, because rainfall is highly seasonal, with most of the approximately 30 inches (76 cm) of annual precipitation occurring between October and April. Ledson Marsh, which drains into Yulupa Creek, retains some smaller pools of water throughout most of the year. The highest elevation in the park is the top of Bennett Mountain, 1,887 feet (575 m).

The entirety of Annadel was below the ocean floor as recently as twelve million years ago, around which time massive uplift and volcanic action formed the massif which comprises the park of today. Elevations in Annadel range from about 360 to 1,880 feet (110 to 570 m) above sea level. Slopes within Annadel commonly range from 15 to 30 percent, but it is not uncommon to encounter slopes up to 70 percent on steep slopes above drainages which are covered in douglas fir forest. One of the major soil associations within the park is Goulding cobbly clay loam, which contains roughly 25 percent cobblestones with some basaltic exposures, evidence of the volcanic origins of the Sonoma Mountains. Typical soil depths are 35 to 50 centimetres (14 to 20 in). Much of the soil type in the Yulupa Creek riparian zone consists of Laniger loam, with rhyolite outcrops, another relic of the igneous history.