1969 (S02E21)

Because of a powerful solar flare, the stargate propels the SG-1 team back in time to 1969, where they emerge into a top-secret military facility and are intercepted by a sentry. Capt. Samantha Carter is frisked by the young lieutenant, who discovers a letter that Gen. George Hammond gave to her. The young man is astonished by the letter's contents. As the team is transported to a more secure location for further interrogation, the young lieutenant helps them escape. He explains that the letter appeared to be from himself, many years in the future. His name is George Hammond. Desperate to find the stargate so they can return to the present, the team seeks out Catherine, who they believe might know its location. Hitchhiking to see her in New York, they are picked up by Michael and Jenny, two friendly flower children on their way to Woodstock. The hippies immediately warm to the team's fugitive appearance. Carter discovers that Hammond's note includes the date of the next solar flare, and they race to the stargate before their chance of leaving the past is lost for good. (Metro-Goldwyn-Mayer (MGM))