3/24:  Sonoma County’s interim public health officer today ordered the closure of all parks in Sonoma County to further enforce the county’s shelter-in-place directive during the COVID-19 emergency. The closure goes into effect March 24 and remains in effect until further notice. Press Release
The closure applies to all agencies and jurisdictions operating parks and open spaces in Sonoma County, including city, county, state and federal parklands and recreational lands operated by private groups and nonprofits. 
The order comes after parks, trails and beaches countywide were crowded with visitors during the initial days of the shelter-in-place orders issued by the county and state. Parking areas and surrounding roads were filled with cars, and visitors gathered on trails, in parking areas, at picnic sites and in other common areas, despite orders to practice social distancing outdoors. FAQ's. (These are from the City of Santa Rosa, but apply to Sebastopol parks as well)