1715
On September 16th, 1715, at exactly 11:36 AM, Marty McFly Jr. arrived in Hill Valley California in the Time Train. Or at least, the wooded country that would become Hill Valley in the next century. Marty Jr. left the Time Train in a hidden area. He found Doc living amongst Indians in approximately the area that would become Hill Valley in the next 150 years…but not before he ran afoul of the local Indian bully, Mighty Condor Tannen and his gang. Mighty Condor challenged Marty Jr. to a duel for the day after next. To make him go through with it, Mighty Condor betrayed Doc and kidnapped him. Marty Jr. had no choice but to break into the Tannen teepee and rescue Doc. A chase between them and the Indians ensued, with Marty Jr. competently firing a bow and arrow to wound Mighty Condor as they flew on the Skaverboard through the Indian encampment. Using that Skaverboard to get away, the pair transported themselves back to the Time Train. Then, Marty Jr. and Doc activated the time machine and returned to 2015.
Back in the present, Doc left Marty Jr. and headed off for another time traveling adventure. When asked if he was going back to the future, Doc said, "Nope. Already been there." And with that, the Time Train disappeared into the portal with a flash of electricity and flame.