19th Century
From Trekipedia
1893
- August 13: Data, Picard, Riker, Crusher, and Troi are transported back in time from Devidia II on Stardate 45965.3 to San Francisco while pursuing a group of Devidians that is preying upon Humans in the past. Data's head is separated from his body; while his body returns to 2368, his head remains in a cave under the Presidio, where it will remain until it is discovered in 2368 as part of a predestination paradox.[1]