Twin Pines Mall, later known as Lone Pine Mall, was the location that Dr. Emmett Brown chose to show Marty McFly the new DeLorean time machine he had invented. At 1:21 a.m. on October 26, 1985, Doc's dog, Einstein, becomes the world's first time traveler leaving behind a pair of fire trails after the DeLorean accelerated to the necessary 88 miles per hour.
During the experiment, Doc became nostalgic and remembered that Otis Peabody used to own the land on which the mall sat in 1985. He noted that Peabody bred pine trees as a hobby.
When Marty traveled to 1955, he accidentally ran over one of a pair of pine trees in Peabody's front yard. When Marty returned to 1985, there was only one pine tree at the front of the mall and as a result the mall's name was changed to Lone Pine Mall.
This was also an important location because it was where Doc was shot by Libyan terrorists until Marty gave him the letter forewarning of it.