“Shasta Lake evacuated accidentally” is probably what the author meant.
“Thousands in Shasta Lake evacuated accidentally” means thousands of people accidentally emptied their bowels.
“Thousands in Shasta Lake evacuated accidentally” means thousands of people accidentally emptied their bowels.
Meaning 2: "To clear (a place) of inmates, etc., (a country) of inhabitants, troops, wild beasts."
Supported by the quotation "Evacuating the Kingdom of all Foreign Troops"
Meaning 8a: "To clear out, remove (inhabitants, inmates, or troops)."
Meaning 8b: "To remove (inhabitants of an area liable to aerial bombing or other hazards) to safer surroundings"
Supported by quotations "He was evacuating the garrison and Egyptian inhabitants of that place" and "Mr. Greenwood and others strongly appealed to the Prime Minister to evacuate children at once"
[1]: http://www.oed.com/view/Entry/65161?redirectedFrom=evacuate#...
To evacuate is to clear something out, not just to leave.
edit: or "Thousands in Shasta Lake were accidentally evacuated" ?