It was formed from the northwestern portion of Trinity County, and originally included all of the northwestern part of the state, from the Mad River in the south to Oregon in the north, from the Pacific Ocean in the west to the middle of what is now Siskiyou County in the east.

The "Klamath and Salmon River Indian "War""and the 1858-1864 "Bald Hills War" involved European-American vigilantes hunting down and killing most indigenous adult males and killing, capturing, or enslaving women and children.

Many of the captive indigenous subsequently died of starvation and exposure at Fort Humboldt.

[2] The European-American settler's economy suffered from the effects of the Indian "wars", which disrupted the supplies to the settlements from the coastal towns.

Worse still was the devastating effects of the Great Flood of 1862 which swept away the riverside settlements, mining works and ferries.