John Dagget, owner of the Black Bear Mine and one time lieutenant governor of California, in 1918, wrote a letter to Miss Claire Mills, clarifying his recollection of the origin of the name Etna.
When Dagget came to the Salmon River country in 1854, there was no town at the present site of Etna. There was an Aetna Mill, owned and operated by the Davidson brothers, Charles McDermit and others who constructed a grist mill, brewery and hotel. This little settlement was washed away by a flood of Whiskey Creek during the winter of 1860-61. This area became known as "Old Etna".
About a mile northeast of "Old Etna", the settlement of "Rough and Ready" had been established prior to the flood of 1860-61, and it became the main site of commerce in that area of Scott Valley. There was already a town called "Rough and Ready" in Nevada County, so the Post Office encouraged the name change to Etna.
from The Siskiyou County Museum and Historical Society