The plaque text:
By the early 1850s, newly arrived white settlers had moved into the Humboldt Bay Area, causing conflict with the native inhabitants. To protect both Indians and settlers, Fort Humboldt was established in 1853 and operated until 1866. It became a focal point in the violent struggle between two cultures. Many Native Americans were assembled here before removal to reservations.
California Registered Historical Plaque No. 154.
Plaque placed buy the state Department of Parks and Recreation in cooperation with the Ancient and Honorable Order of E Clampus Vitus, Eureka Chapter No. 101, May 10, 1980.
That's one version of the fort's role in the genocide along California' North Coast. For context, here's another, from Humboldt's alternative weekly, the North Coast Journal: "Genocide and Extortion."